Income Taxes - Summary of Income Tax Reconciliation (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Federal income tax at expected statutory rate									$ 69,235	$ 88,458	$ 81,683
State income tax expense, net of federal tax effect									23,851	21,046	19,197
Tax-exempt interest, net of interest incurred to carry tax-exempt securities									(3,974)	(5,245)	(5,308)
Bank owned life insurance									(1,734)	(2,568)	(2,343)
Tax credits from securities and other investments									(20,798)	(27,037)	(25,954)
FDIC insurance premium									3,318	0	0
Impact of the Tax Act									(2,274)	15,441	0
Other, net									641	736	(2,041)
Income tax expense	$ 18,074	$ 18,046	$ 18,961	$ 13,184	$ 34,958	$ 17,088	$ 20,714	$ 18,071	$ 68,265	$ 90,831	$ 65,234