Income Taxes - Reconciliation of Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
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	$ 83,308	$ 77,977	$ 110,493
Change in tax rate	0	0	10,095
Tax-exempt interest	(123)	(1,305)	(2,278)
(Decrease) increase in unrecognized tax benefits	(3,088)	3,088	0
Other, net	(213)	3,336	386
Income tax expense	$ 79,884	$ 83,096	$ 118,696