Income Taxes - Reconciliation of Tax Rate (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Reconciliation of statutory tax to effective tax
Federal statutory tax rate	$ 39,472	$ 42,501	$ 48,971	$ 90,357
REIT and other non-taxable income	(39,171)	(40,510)	(48,135)	(75,482)
State income taxes	72	179	(23)	2,180
Federal benefit of state tax deduction	(25)	(63)	8	(763)
Valuation allowance		1,618		2,873
Other	358	67	(21)	578
Effective tax rate	$ 706	$ 3,792	$ 800	$ 19,743
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)	(34.70%)	(33.30%)	(34.40%)	(29.20%)
State income taxes (as a percent)	0.10%	0.10%		0.80%
Federal benefit of state tax deduction (as a percent)	(0.10%)	(0.10%)		(0.30%)
Valuation allowance (as a percent)		1.30%		1.10%
Other (as a percent)	0.30%	0.10%		0.20%
Effective tax rate (as a percent)	0.60%	3.10%	0.60%	7.60%