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Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Narrative (Details)

v3.10.0.1
Summary of Significant Accounting Policies - Narrative (Details)
 12 Months Ended
Dec. 31, 2018
USD ($)
financial_institutions
Dec. 31, 2017
USD ($)
Dec. 31, 2016
Easement agreements, term 10 years Ìý Ìý
Unrecognized tax benefits $ 0 $ 0 Ìý
Cash and Cash Equivalents | Customer Concentration Risk Ìý Ìý Ìý
Number of customers | financial_institutions 2 Ìý Ìý
Sales Revenue, Net | Customer Concentration Risk Ìý Ìý Ìý
Concentration risk, percentage 31.30% 26.50% 23.70%
Accounting Standards Update 2018-02 Ìý Ìý Ìý
Cumulative adjustment from AOCI $ 200,000 Ìý Ìý
Maximum Ìý Ìý Ìý
Royalty payment arrangement, term 3 months Ìý Ìý
Lease terms of payment arrangements 10 years Ìý Ìý
Minimum Ìý Ìý Ìý
Royalty payment arrangement, term 1 month Ìý Ìý
Lease terms of payment arrangements 1 month Ìý Ìý