Income Taxes - Reconciliation of Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Computed at the statutory rate	$ 67,143	$ 63,442	$ 55,875
State income taxes, net of federal tax benefit	6,402	5,860	5,015
Discrete items related to ASU 2016-09	375	(38)	(2,439)
Tax exempt interest income	(6,726)	(4,390)	(3,168)
Tax exempt earnings on BOLI	(1,214)	(852)	(869)
Federal tax credits	(2,177)	(939)	(3,003)
Other differences, net	1,087	1,182	(1,053)
Provision for income taxes	$ 64,890	$ 64,265	$ 50,358