Income Taxes - Reconciliation of Tax Rate (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2017
Reconciliation of statutory tax to effective tax
Federal statutory tax rate	$ 26,199	$ (15,329)
REIT and other non-taxable income	(24,501)	9,914
State income taxes	558	(1,779)
Federal benefit of state tax deduction	(117)	374
Other	91	91
Total income tax provision	$ 2,230	$ (6,729)
Reconciliation of statutory tax rate to effective tax rate
Federal statutory tax rate (as a percent)	21.00%	21.00%	35.00%
REIT and other non-taxable income (as a percent)	(19.60%)	(13.60%)
State income taxes (as a percent)	0.40%	2.40%
Federal benefit of state tax deduction (as a percent)	(0.10%)	(0.50%)
Other (as a percent)	0.10%	(0.10%)
Effective tax rate (as a percent)	1.80%	9.20%