Investments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Equity Method Investments and Joint Ventures [Abstract]
Advantage Joint Venture	$ 68,891		$ 68,891		$ 0
White Cliffs Interest	10,677		10,677		11,151
Investments	79,568		79,568		$ 11,151
Schedule of Equity Method Investments [Line Items]
Total Investment Income	1,641	$ 1,146	2,706	$ 2,439
Capitalized acquisition related expenses	1,700		1,700
Advantage Joint Venture
Schedule of Equity Method Investments [Line Items]
Total Investment Income	405	0	405	0
Noncurrent Assets	4,036		4,036
Noncurrent Assets	131,294		131,294
Current Liabilities	1,275		1,275
Operating Revenues			3,088
Operating Expenses			2,242
Net Income			846
White Cliffs Interest
Schedule of Equity Method Investments [Line Items]
Total Investment Income	1,119	1,146	2,184	2,439
Other
Schedule of Equity Method Investments [Line Items]
Total Investment Income	$ 117	$ 0	117	$ 0
Investment operator fees			$ 700