This item represents the amount of net sales proceeds received on disposal of an equity method investment.

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The net of the gross additions and gross reductions to the investment in and advance to the affiliate.

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Equity Method Investments and Membership Interests in Joint Ventures (Schedule of Equity Method Investments) (Details) - USD ($) $ in Thousands	3 Months Ended			12 Months Ended
	Sep. 30, 2015	Sep. 30, 2013	Jun. 30, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]
Beginning Balance				$ 235,842	$ 221,456	$ 242,215
Advances to (distributions from) affiliates, net				(18,360)	4,054	788
Equity in comprehensive income (loss)				7,979	10,332	7,400
Impairment of equity investment				(21,325)	0	(28,947)
Sale of equity investment				(2,259)
Ending Balance				201,877	235,842	221,456
Knight Hawk [Member]
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]
Beginning Balance				158,477	152,806	149,063
Advances to (distributions from) affiliates, net				(29,862)	(12,603)	(13,536)
Equity in comprehensive income (loss)				22,977	18,274	17,279
Impairment of equity investment				0		0
Ending Balance				151,592	158,477	152,806
DTA [Member]
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]
Beginning Balance				13,738	14,137	15,462
Advances to (distributions from) affiliates, net				3,207	3,774	3,644
Equity in comprehensive income (loss)				(3,706)	(4,173)	(4,969)
Impairment of equity investment						0
Ending Balance				13,239	13,738	14,137
Millennium [Member]
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]
Beginning Balance				40,223	35,894	32,214
Advances to (distributions from) affiliates, net				7,052	6,742	6,476
Equity in comprehensive income (loss)				(9,686)	(2,413)	(2,796)
Impairment of equity investment				0
Ending Balance				37,589	40,223	35,894
Tongue River [Member]
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]
Beginning Balance				20,740	18,419	14,697
Advances to (distributions from) affiliates, net				913	2,541	4,004
Equity in comprehensive income (loss)				(328)	(220)	(282)
Impairment of equity investment	$ (21,300)			(21,325)		0
Ending Balance				0	20,740	18,419
DKRW [Member]
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]
Beginning Balance						15,515
Advances to (distributions from) affiliates, net				0
Equity in comprehensive income (loss)						(1,832)
Impairment of equity investment		$ 13,700				(13,683)
Tenaska [Member]
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]
Beginning Balance						15,264
Impairment of equity investment			$ 15,300	0		(15,264)
Ending Balance				0
Other Affiliates [Member]
Investments in and Advances to Affiliates, at Fair Value [Roll Forward]
Beginning Balance				2,664	200
Advances to (distributions from) affiliates, net				330	3,600	200
Equity in comprehensive income (loss)				(1,278)	(1,136)
Impairment of equity investment				0		0
Sale of equity investment				(2,259)
Ending Balance				$ (543)	$ 2,664	$ 200