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    
Unrecognized tax benefits $ 0 $ 0  
Cash and Cash Equivalents | Customer Concentration Risk      
Number of customers | financial_institutions 2    
Sales Revenue, Net | Customer Concentration Risk      
Concentration risk, percentage 31.30% 26.50% 23.70%
Accounting Standards Update 2018-02      
Cumulative adjustment from AOCI $ 200,000    
Maximum      
Royalty payment arrangement, term 3 months    
Lease terms of payment arrangements 10 years    
Minimum      
Royalty payment arrangement, term 1 month    
Lease terms of payment arrangements 1 month