Income Taxes - Reconciliation of Tax Rate (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Reconciliation of statutory tax to effective tax
Federal statutory tax rate	$ 28,556	$ 25,291	$ 44,692	$ 47,897
REIT and other non-taxable income	(26,013)	(23,157)	(42,172)	(43,500)
State income taxes	666	558	660	1,151
Federal benefit of state tax deduction	(140)	(118)	(139)	(242)
Other	464	769	826	893
Total income tax provision	$ 3,533	$ 3,343	$ 3,867	$ 6,199
Reconciliation of statutory tax rate to effective tax rate
Federal statutory tax rate (as a percent)	21.00%	21.00%	21.00%	21.00%
REIT and other non-taxable income (as a percent)	(19.10%)	(19.20%)	(19.80%)	(19.10%)
State income taxes (as a percent)	0.50%	0.50%	0.30%	0.50%
Federal benefit of state tax deduction (as a percent)	(0.10%)	(0.10%)	(0.10%)	(0.10%)
Other (as a percent)	0.30%	0.60%	0.40%	0.40%
Effective tax rate (as a percent)	2.60%	2.80%	1.80%	2.70%