Income Taxes - Reconciliation of Income Tax Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Income Tax Disclosure [Abstract]
Computed at the statutory rate	$ 20,560	$ 12,620
State income taxes, net of federal tax benefit	2,063	1,345
Discrete items related to ASU 2016-09	26	(26)
Tax exempt interest income	(1,421)	(961)
Tax exempt earnings on BOLI	(319)	(179)
Federal tax credits	(1,034)	(729)
Other differences, net	819	328
Provision for income taxes	$ 20,694	$ 12,398