Summary of Significant Accounting Policies - Adoption of ASU 2014-09 (Details) - USD ($) $ / shares in Units, $ in Thousands |
3 Months Ended | 6 Months Ended | |||
|---|---|---|---|---|---|
Jun. 30, 2018 |
Jun. 30, 2017 |
Jun. 30, 2018 |
Jun. 30, 2017 |
Dec. 31, 2017 |
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| Condensed Consolidated Statements of Income: | Ìý | Ìý | Ìý | Ìý | Ìý |
| Revenue | $ 73,844 | $ 32,293 | $ 133,851 | $ 62,700 | Ìý |
| Taxes, other than income taxes | 113 | 62 | 257 | 117 | Ìý |
| Income taxes | 13,162 | 10,035 | 23,982 | 19,673 | Ìý |
| Net income | $ 52,503 | $ 20,350 | $ 96,294 | $ 39,609 | Ìý |
| Net income per Sub-share Certificate (in usd per share) | $ 6.73 | $ 2.58 | $ 12.33 | $ 5.02 | Ìý |
| ASSETS | Ìý | Ìý | Ìý | Ìý | Ìý |
| Accrued receivables | $ 35,664 | Ìý | $ 35,664 | Ìý | $ 17,773 |
| Deferred tax liability | (114) | Ìý | (114) | Ìý | (114) |
| Liabilities and Capital: | Ìý | Ìý | Ìý | Ìý | Ìý |
| Unearned revenue | 11,313 | Ìý | 11,313 | Ìý | 8,364 |
| Other taxes payable | Ìý | Ìý | Ìý | Ìý | 0 |
| Net proceeds from all sources | $ 153,510 | Ìý | $ 153,510 | Ìý | 105,902 |
| As reported in prior year | Ìý | Ìý | Ìý | Ìý | Ìý |
| Condensed Consolidated Statements of Income: | Ìý | Ìý | Ìý | Ìý | Ìý |
| Revenue | Ìý | $ 27,349 | Ìý | $ 51,577 | Ìý |
| Taxes, other than income taxes | Ìý | 762 | Ìý | 1,422 | Ìý |
| Income taxes | Ìý | 8,030 | Ìý | 15,258 | Ìý |
| Net income | Ìý | $ 16,711 | Ìý | $ 31,597 | Ìý |
| Net income per Sub-share Certificate (in usd per share) | Ìý | $ 2.12 | Ìý | $ 4.00 | Ìý |
| ASSETS | Ìý | Ìý | Ìý | Ìý | Ìý |
| Accrued receivables | Ìý | Ìý | Ìý | Ìý | 18,206 |
| Deferred tax asset | Ìý | Ìý | Ìý | Ìý | 6,992 |
| Liabilities and Capital: | Ìý | Ìý | Ìý | Ìý | Ìý |
| Unearned revenue | Ìý | Ìý | Ìý | Ìý | 41,375 |
| Other taxes payable | Ìý | Ìý | Ìý | Ìý | 433 |
| Net proceeds from all sources | Ìý | Ìý | Ìý | Ìý | 79,997 |
| Retrospective Adjustment | Accounting Standards Update 2014-09 | Ìý | Ìý | Ìý | Ìý | Ìý |
| Condensed Consolidated Statements of Income: | Ìý | Ìý | Ìý | Ìý | Ìý |
| Revenue | Ìý | $ 4,944 | Ìý | $ 11,123 | Ìý |
| Taxes, other than income taxes | Ìý | (700) | Ìý | (1,305) | Ìý |
| Income taxes | Ìý | 2,005 | Ìý | 4,415 | Ìý |
| Net income | Ìý | $ 3,639 | Ìý | $ 8,012 | Ìý |
| Net income per Sub-share Certificate (in usd per share) | Ìý | $ 0.46 | Ìý | $ 1.02 | Ìý |
| ASSETS | Ìý | Ìý | Ìý | Ìý | Ìý |
| Accrued receivables | Ìý | Ìý | Ìý | Ìý | (433) |
| Deferred tax liability | Ìý | Ìý | Ìý | Ìý | (7,106) |
| Liabilities and Capital: | Ìý | Ìý | Ìý | Ìý | Ìý |
| Unearned revenue | Ìý | Ìý | Ìý | Ìý | (33,011) |
| Other taxes payable | Ìý | Ìý | Ìý | Ìý | (433) |
| Net proceeds from all sources | Ìý | Ìý | Ìý | Ìý | $ 25,905 |
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- Definition Liabilities and Capital [Abstract] No definition available.
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- References No definition available.
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- Definition Amount, after allocation of valuation allowances and deferred tax liability, of deferred tax asset attributable to deductible differences and carryforwards, with jurisdictional netting. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition Amount, after deferred tax asset, of deferred tax liability attributable to taxable differences with jurisdictional netting. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition The carrying amount of consideration received or receivable as of the balance sheet date on potential earnings that were not recognized as revenue in conformity with GAAP, and which are expected to be recognized as such within one year or the normal operating cycle, if longer, including sales, license fees, and royalties, but excluding interest income. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition The amount of net income or loss for the period per each share in instances when basic and diluted earnings per share are the same amount and reported as a single line item on the face of the financial statements. Basic earnings per share is the amount of net income or loss for the period per each share of common stock or unit outstanding during the reporting period. Diluted earnings per share includes the amount of net income or loss for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period. No definition available.
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- References No definition available.
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- Definition Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition The portion of profit or loss for the period, net of income taxes, which is attributable to the parent. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition Amount due from parties in nontrade transactions, classified as other. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition A segregation of retained earnings which is available for dividend distribution. Earnings not paid out as dividends but instead reinvested in the core business or used to pay off debt. Unappropriated profit is part of shareholder equity. Also called cumulative distributions or earned surplus or accumulated earnings or unappropriated profit. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss). Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition All taxes not related to income of the entity or excise or sales taxes levied on the revenue of the entity that are not reported elsewhere. These taxes could include production, real estate, personal property, and pump tax. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition Carrying value as of the balance sheet date of obligations incurred and payable for statutory income, sales, use, payroll, excise, real, property and other taxes. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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