Investments in Unconsolidated Joint Ventures - Operations (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Schedule of Equity Method Investments [Line Items]
Revenues	$ 490,339	$ 342,714	$ 1,171,885	$ 932,792
Cost of sales	(447,169)	(321,390)	(1,094,172)	(877,005)
Operating income (loss)	43,170	21,324	77,713	55,787
Unconsolidated joint venture income	1,160	1,435	2,622	3,810
Joint Ventures
Schedule of Equity Method Investments [Line Items]
Revenues	5,368	5,397	13,830	14,675
Cost of sales	(2,781)	(2,521)	(7,936)	(7,043)
Operating income (loss)	$ 2,587	$ 2,876	$ 5,894	$ 7,632