Investments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Equity Method Investments and Joint Ventures [Abstract]
Advantage Joint Venture	$ 69,325		$ 69,325		$ 0
White Cliffs Interest	10,423		10,423		11,151
Investments	79,748		79,748		$ 11,151
Capitalized acquisition related expenses	1,700		1,700
Schedule of Equity Method Investments [Line Items]
Total Investment Income	1,633	$ 1,070	4,339	$ 3,509
Advantage Joint Venture
Schedule of Equity Method Investments [Line Items]
Total Investment Income	416	0	821	0
Current Assets	5,874		5,874
Noncurrent Assets	130,721		130,721
Current Liabilities	1,255		1,255
Operating Revenues	3,186		6,274
Operating Expenses	2,314		4,556
Income Before Taxes	872		1,718
Income Tax Expense	20		20
Net Income	852		1,698
White Cliffs Interest
Schedule of Equity Method Investments [Line Items]
Total Investment Income	1,042	1,070	3,226	3,509
Other
Schedule of Equity Method Investments [Line Items]
Total Investment Income	$ 175	$ 0	292	$ 0
Investment operator fees			$ 700