Equity Method Investments Halley & Mellowes (HMA) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Equity Method Investments [Line Items]
Proceeds from Divestiture of Interest in Joint Venture									$ 0
Equity Method Investment, Realized Gain (Loss) on Disposal									0	$ 8,300
Equity in income (loss) and impairment of investees	$ 3,513	$ 1,234	$ (15,232)	$ 618	$ 11,553	$ 2,827	$ (616)	$ 2,676	$ (9,867)	16,440	$ (242)
HMA [Domain]
Schedule of Equity Method Investments [Line Items]
Proceeds from Divestiture of Interest in Joint Venture										18,000	0
Equity Method Investment, Realized Gain (Loss) on Disposal										8,300
Equity in income (loss) and impairment of investees										$ 2,200	$ 3,100