Investments in Unconsolidated Joint Ventures - Operations (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Schedule of Equity Method Investments [Line Items]
Revenues	$ 422,692	$ 325,653	$ 681,546	$ 590,078
Cost of sales	(394,457)	(304,470)	(647,003)	(555,615)
Operating income (loss)	28,235	21,183	34,543	34,463
Unconsolidated joint venture income	1,213	1,194	1,462	2,375
Joint Ventures
Schedule of Equity Method Investments [Line Items]
Revenues	5,073	5,311	8,462	9,278
Cost of sales	(3,045)	(2,597)	(5,155)	(4,522)
Operating income (loss)	$ 2,028	$ 2,714	$ 3,307	$ 4,756