Income Taxes - Reconciliation of Tax Rate (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Reconciliation of statutory tax to effective tax
Federal statutory tax rate	$ 46,439	$ 39,472	$ 82,094	$ 48,971
REIT and other non-taxable income	(37,000)	(39,171)	(73,425)	(48,135)
State income taxes	20	72	(119)	(23)
Federal benefit of state tax deduction	(7)	(25)	42	8
Other		358	(123)	(21)
Total	9,452	$ 706	8,469	$ 800
Investment in unconsolidated entities	$ 229,539		$ 229,539		$ 204,605
Reconciliation of statutory tax rate to effective tax rate
Federal statutory tax rate (as a percent)	35.00%	35.00%	35.00%	35.00%
REIT and other non-taxable income (as a percent)	(27.90%)	(34.70%)	(31.20%)	(34.40%)
State income taxes (as a percent)		0.10%	(0.10%)
Federal benefit of state tax deduction (as a percent)		(0.10%)
Other (as a percent)		0.30%	(0.10%)
Effective tax rate (as a percent)	7.10%	0.60%	3.60%	0.60%
Investor entity which owns equity in an online real estate auction company
Reconciliation of statutory tax to effective tax
Total	$ 9,900		$ 9,900
Investment in unconsolidated entities	$ 25,700		$ 25,700