Equity Method Investments - Narrative (Details) - USD ($)		3 Months Ended								12 Months Ended
	Feb. 10, 2014	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jan. 20, 2010
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments		$ 3,788,000	$ (41,000)	$ 4,860,000	$ 314,000	$ 20,693,000	$ 5,603,000	$ 9,791,000	$ 6,625,000	$ 8,921,000	$ 42,712,000	$ 15,502,000
Equity method investments		17,232,000				19,584,000				17,232,000	19,584,000
Purchase, contributions and advances to equity method investees										2,128,000	6,631,000	0
Purchase of membership interest, note payable outstanding		$ 28,025,000				$ 15,910,000				28,025,000	15,910,000
Impairment of equity method investments										$ 0	$ 0	0
Clean Coal Solutions (CCS)
Schedule of Equity Method Investments [Line Items]
Ownership interest, percent		42.50%				42.50%				42.50%	42.50%
Preferred return to third party unitholders										15.00%
Preferred unitholder, redemption period										10 years
Preferred unitholder, redemption notice period										180 days
Voting interest		50.00%								50.00%
Earnings from equity method investments										$ 8,651,000	$ 43,584,000	13,813,000
Equity method investments		$ 0				$ 0				0	0	0	$ 0
Losses related to VIEs, attributable to noncontrolling interest										10,675,000	11,023,000	0
Clean Coal Solutions (CCS) | Cash distributions
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments										(8,651,000)	(43,584,000)	(13,813,000)
Equity method investments		8,651,000				43,584,000				8,651,000	43,584,000	13,813,000	0
Clean Coal Solutions (CCS) | Memo Account: Cash distributions and equity loss in (excess) of investment balance
Schedule of Equity Method Investments [Line Items]
Earnings from equity method investments										0	0	0
Equity method investments		$ 3,263,000				(29,877,000)				$ 3,263,000	(29,877,000)	(12,906,000)	$ (8,003,000)
NexGen Refined Coal, LLC (NexGen)
Schedule of Equity Method Investments [Line Items]
Ownership interest, percent		42.50%								42.50%
GSFS Investments I Corp. (GSFS)
Schedule of Equity Method Investments [Line Items]
Ownership interest, percent		15.00%								15.00%
Clean Coal Solutions Services (CCSS)
Schedule of Equity Method Investments [Line Items]
Ownership interest, percent		50.00%								50.00%				50.00%
Earnings from equity method investments										$ 4,838,000	3,625,000	1,689,000
Equity method investments		$ 3,968,000				4,149,000				3,968,000	4,149,000
Losses related to VIEs, attributable to noncontrolling interest										$ 213,746,000	132,237,000	77,814,000
RMC6, LLC (RCM6)
Schedule of Equity Method Investments [Line Items]
Ownership interest, percent	24.95%	24.95%								24.95%
Earnings from equity method investments										$ (4,568,000)	(4,497,000)	$ 0
Equity method investments		$ 13,264,000				15,435,000				13,264,000	15,435,000
Purchase, contributions and advances to equity method investees	$ 2,400,000									2,400,000	4,200,000
Purchase of membership interest, note payable issued	$ 13,300,000
Debt instrument, term	7 years
Purchase of membership interest, note payable outstanding		14,200,000				$ 14,200,000				14,200,000	14,200,000
Amount by which investment exceeded proportionate share of investee's net assets		$ 11,900,000								11,900,000
Earnings (loss) from equity method investment for depreciation and amortization related to investment basis difference										$ 1,900,000	$ 1,700,000