Investments in Unconsolidated Joint Ventures Investments in Unconsolidated Joint Ventures - Operations (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]
Total operating revenue	$ 623,283	$ 490,304	$ 422,633	$ 258,854	$ 473,221	$ 342,628	$ 325,059	$ 261,295	$ 1,796,528	$ 1,406,040	$ 1,104,052
Cost of sales									(1,658,572)	(1,312,072)	(1,023,805)
Operating income									137,956	93,968	80,247
Other assets, net	21,164				17,283				21,164	17,283
Total assets	2,061,104				2,011,280				2,061,104	2,011,280
Accounts payable	58,799				74,282				58,799	74,282
Accrued expenses	111,491				92,919				111,491	92,919
Total liabilities and equity	2,061,104				2,011,280				2,061,104	2,011,280
Equity in income of unconsolidated joint ventures									3,661	5,606	3,239
Joint Ventures
Schedule of Equity Method Investments [Line Items]
Total operating revenue									20,003	21,156	12,314
Cost of sales									(11,913)	(10,407)	(5,842)
Operating income									8,090	10,749	$ 6,472
Cash	12,802				10,208				12,802	10,208
Loans held for sale	17,106				18,791				17,106	18,791
Accounts receivable	2,791				764				2,791	764
Other assets, net	128				56				128	56
Total assets	32,827				29,819				32,827	29,819
Accounts payable	779				694				779	694
Accrued expenses	1,532				1,026				1,532	1,026
Credit lines payable	18,312				17,748				18,312	17,748
Other liabilities	31				17				31	17
Members equity	12,173				10,334				12,173	10,334
Total liabilities and equity	$ 32,827				$ 29,819				$ 32,827	$ 29,819