Income Taxes - Reconciliation of Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Computed at the statutory rate	$ 55,875	$ 54,223	$ 50,203
State income taxes, net of federal tax benefit	5,015	1,582	2,121
Discrete items related to ASU 2016-09	(2,439)	(1,480)	0
Tax exempt interest income	(3,168)	(4,209)	(4,207)
Tax exempt earnings on BOLI	(869)	(926)	(905)
Federal tax credits	(3,003)	(1,586)	(1,161)
Impact of DTA remeasurement	0	11,471	0
Other differences, net	(1,053)	2,908	573
Provision for income taxes	$ 50,358	$ 61,983	$ 46,624