Income Taxes - Reconciliation of Statutory Income Tax Provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Expected tax at statutory rate	$ 95,828	$ 186,274	$ 144,708
Non-taxable REIT income	(83,022)	(170,811)	(131,112)
State and local tax expense - net of federal benefit	2,385	2,306	2,399
Change in valuation allowance	(1,052)	159	(845)
Tax credits/true-up	(6,016)	(5,956)	(312)
Remeasurement of deferred balances	0	(8,460)	0
Miscellaneous	1,121	113	1,009
Total provision	$ 9,244	$ 3,625	$ 15,847
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Expected tax at statutory rate	21.00%	35.00%	35.00%
Non-taxable REIT income	(18.20%)	(32.10%)	(31.70%)
State and local tax expense - net of federal benefit	0.50%	0.40%	0.60%
Change in valuation allowance	(0.20%)	0.00%	(0.20%)
Tax credits/true-up	(1.30%)	(1.10%)	(0.10%)
Remeasurement of deferred balances	0.00%	(1.60%)	0.00%
Miscellaneous	0.20%	0.00%	0.20%
Total provision	2.00%	0.60%	3.80%