Significant Accounting Policies Significant Accounting Policies (Accelerated Depreciation) (Details Textuals 2) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Finite-Lived Intangible Assets [Line Items]
Accelerated depreciation		$ 846,043	$ 531,660	$ 592,972
Riley Ridge gas processing facility and related assets
Finite-Lived Intangible Assets [Line Items]
Accelerated depreciation	$ 591,000
Helium production rights intangible asset
Finite-Lived Intangible Assets [Line Items]
Accelerated depreciation	$ 55,300