Income Taxes - Reconciliation of Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of the provision for income taxes, with amounts determined by applying the statutory federal income tax rate to pre-tax income
Income tax at statutory rate	$ 77,388	$ 83,308	$ 77,977
Tax-exempt interest	0	(123)	(1,305)
(Decrease) increase in unrecognized tax benefits	0	(3,088)	3,088
Other, net	(2,177)	(213)	3,336
Income tax expense	$ 75,211	$ 79,884	$ 83,096