Changes in Equity - Changes in Equity (Details) - USD ($) $ / shares in Units, $ in Thousands |
3 Months Ended | 9 Months Ended | |||||||
|---|---|---|---|---|---|---|---|---|---|
May 03, 2022 |
Sep. 30, 2022 |
Jun. 30, 2022 |
Mar. 31, 2022 |
Sep. 30, 2021 |
Jun. 30, 2021 |
Mar. 31, 2021 |
Sep. 30, 2022 |
Sep. 30, 2021 |
|
| Increase (Decrease) in Stockholders' Equity [Roll Forward] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Beginning balance | Ìý | $ 645,281 | $ 727,876 | $ 651,711 | $ 547,177 | $ 513,935 | $ 485,184 | $ 651,711 | $ 485,184 |
| Beginning balance, treasury stock (in shares) | Ìý | Ìý | Ìý | 11,461 | Ìý | Ìý | Ìý | 11,461 | Ìý |
| Net income | Ìý | 129,837 | 118,894 | $ 97,900 | 83,837 | 57,046 | 50,052 | $ 346,631 | 190,935 |
| Share-based compensation, net of forfeitures | Ìý | 2,091 | 1,811 | 1,481 | Ìý | Ìý | Ìý | Ìý | Ìý |
| Conversion of Sub-shares into shares of common stock | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 0 | Ìý | Ìý |
| Periodic pension costs, net of income taxes | Ìý | 8 | 8 | 8 | 29 | 29 | 28 | 24 | 86 |
| Repurchases of common stock | Ìý | (32,915) | (25,534) | Ìý | (8,689) | (2,504) | Ìý | Ìý | Ìý |
| Ending balance | Ìý | $ 721,170 | 645,281 | $ 727,876 | $ 601,042 | $ 547,177 | $ 513,935 | $ 721,170 | $ 601,042 |
| Ending balance, treasury stock (in shares) | Ìý | 47,311 | Ìý | Ìý | Ìý | Ìý | Ìý | 47,311 | Ìý |
| Dividend paid per common stock (in USD per share) | Ìý | $ 3.00 | Ìý | $ 3.00 | $ 2.75 | Ìý | $ 2.75 | $ 29.00 | $ 8.25 |
| Other comprehensive income - periodic pension costs | Ìý | $ 3 | $ 2 | $ 2 | $ 8 | Ìý | $ 8 | $ 8 | $ 23 |
| Common Stock | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Increase (Decrease) in Stockholders' Equity [Roll Forward] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Beginning balance (in shares) | Ìý | 7,727,916 | 7,745,290 | 7,744,695 | 7,754,523 | 7,756,156 | 0 | 7,744,695 | 0 |
| Beginning balance | Ìý | $ 78 | $ 78 | $ 78 | $ 78 | $ 78 | $ 0 | $ 78 | $ 0 |
| Share-based compensation, net of forfeitures (in shares) | Ìý | Ìý | 104 | 595 | Ìý | Ìý | Ìý | Ìý | Ìý |
| Conversion of sub-shares into shares of common stock (in shares) | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 7,756,156 | Ìý | Ìý |
| Conversion of Sub-shares into shares of common stock | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | $ 78 | Ìý | Ìý |
| Repurchases of common stock (in shares) | Ìý | (19,071) | (17,478) | Ìý | (6,179) | (1,633) | Ìý | Ìý | Ìý |
| Ending balance (in shares) | Ìý | 7,708,845 | 7,727,916 | 7,745,290 | 7,748,344 | 7,754,523 | 7,756,156 | 7,708,845 | 7,748,344 |
| Ending balance | Ìý | $ 78 | $ 78 | $ 78 | $ 78 | $ 78 | $ 78 | $ 78 | $ 78 |
| Sub-share Certificates | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Increase (Decrease) in Stockholders' Equity [Roll Forward] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Beginning balance (in shares) | Ìý | Ìý | Ìý | Ìý | 0 | 0 | 7,756,156 | Ìý | 7,756,156 |
| Conversion of sub-shares into shares of common stock (in shares) | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 7,756,156 | Ìý | Ìý |
| Ending balance (in shares) | Ìý | Ìý | Ìý | Ìý | 0 | 0 | 0 | Ìý | 0 |
| Treasury Stock | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Increase (Decrease) in Stockholders' Equity [Roll Forward] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Beginning balance | Ìý | $ (40,011) | $ (14,617) | $ (15,417) | $ (2,504) | $ 0 | $ 0 | $ (15,417) | $ 0 |
| Beginning balance, treasury stock (in shares) | Ìý | 28,240 | 10,866 | 11,461 | 1,633 | 0 | 0 | 11,461 | 0 |
| Share-based compensation, forfeitures (in shares) | Ìý | Ìý | (104) | (595) | Ìý | Ìý | Ìý | Ìý | Ìý |
| Share-based compensation, net of forfeitures | Ìý | Ìý | $ 140 | $ 800 | Ìý | Ìý | Ìý | Ìý | Ìý |
| Repurchases of common stock (in shares) | Ìý | 19,071 | 17,478 | Ìý | 6,179 | 1,633 | Ìý | Ìý | Ìý |
| Repurchases of common stock | Ìý | $ (32,915) | $ (25,534) | Ìý | $ (8,689) | $ (2,504) | Ìý | Ìý | Ìý |
| Ending balance | Ìý | $ (72,926) | $ (40,011) | $ (14,617) | $ (11,193) | $ (2,504) | $ 0 | $ (72,926) | $ (11,193) |
| Ending balance, treasury stock (in shares) | Ìý | 47,311 | 28,240 | 10,866 | 7,812 | 1,633 | 0 | 47,311 | 7,812 |
| Additional Paid-in Capital | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Increase (Decrease) in Stockholders' Equity [Roll Forward] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Beginning balance | Ìý | $ 3,356 | $ 1,505 | $ 28 | Ìý | Ìý | Ìý | $ 28 | Ìý |
| Share-based compensation, net of forfeitures | Ìý | 2,121 | 1,851 | 1,477 | Ìý | Ìý | Ìý | Ìý | Ìý |
| Ending balance | Ìý | 5,477 | 3,356 | 1,505 | Ìý | Ìý | Ìý | 5,477 | Ìý |
| Accum. Other Comp. Inc/(Loss) | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Increase (Decrease) in Stockholders' Equity [Roll Forward] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Beginning balance | Ìý | (991) | (999) | (1,007) | $ (2,636) | $ (2,665) | $ (2,693) | (1,007) | $ (2,693) |
| Periodic pension costs, net of income taxes | Ìý | 8 | 8 | 8 | 29 | 29 | 28 | Ìý | Ìý |
| Ending balance | Ìý | (983) | (991) | (999) | (2,607) | (2,636) | (2,665) | (983) | (2,607) |
| Retained Earnings | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Increase (Decrease) in Stockholders' Equity [Roll Forward] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Beginning balance | Ìý | 682,849 | 741,909 | 668,029 | 552,239 | 516,522 | 0 | 668,029 | 0 |
| Net income | Ìý | 129,837 | 118,894 | 97,900 | 83,837 | 57,046 | 50,052 | Ìý | Ìý |
| Share-based compensation, net of forfeitures | Ìý | (30) | (180) | (796) | Ìý | Ìý | Ìý | Ìý | Ìý |
| Conversion of Sub-shares into shares of common stock | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | 487,799 | Ìý | Ìý |
| Ending balance | Ìý | 789,524 | 682,849 | 741,909 | 614,764 | 552,239 | 516,522 | $ 789,524 | 614,764 |
| Net Proceeds From All Sources | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Increase (Decrease) in Stockholders' Equity [Roll Forward] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Beginning balance | Ìý | Ìý | Ìý | Ìý | 0 | 0 | 487,877 | Ìý | 487,877 |
| Conversion of Sub-shares into shares of common stock | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | (487,877) | Ìý | Ìý |
| Ending balance | Ìý | Ìý | Ìý | Ìý | 0 | 0 | 0 | Ìý | $ 0 |
| Dividend Paid | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Increase (Decrease) in Stockholders' Equity [Roll Forward] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Dividends paid | Ìý | $ (23,132) | $ (23,188) | (23,224) | $ (21,312) | $ (21,329) | (21,329) | Ìý | Ìý |
| Dividend paid per common stock (in USD per share) | Ìý | $ 3.00 | $ 3.00 | Ìý | $ 2.75 | $ 2.75 | Ìý | Ìý | Ìý |
| Dividend Paid | Retained Earnings | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Increase (Decrease) in Stockholders' Equity [Roll Forward] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Dividends paid | Ìý | $ (23,132) | $ (23,188) | $ (23,224) | $ (21,312) | $ (21,329) | $ (21,329) | Ìý | Ìý |
| Special Dividend Paid | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Increase (Decrease) in Stockholders' Equity [Roll Forward] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Dividends paid | Ìý | Ìý | (154,586) | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Dividend paid per common stock (in USD per share) | $ 20.00 | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Special Dividend Paid | Retained Earnings | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Increase (Decrease) in Stockholders' Equity [Roll Forward] | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |
| Dividends paid | Ìý | Ìý | $ (154,586) | Ìý | Ìý | Ìý | Ìý | Ìý | Ìý |