Income Taxes - Summary of Income Tax Reconciliation (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Federal income tax at expected statutory rate									$ 95,927	$ 69,235	$ 88,458
State income tax expense, net of federal tax effect									32,581	23,851	21,046
Tax-exempt interest, net of interest incurred to carry tax-exempt securities									(3,118)	(3,974)	(5,245)
Bank owned life insurance									(1,637)	(1,734)	(2,568)
Tax credits from securities and other investments									(11,636)	(20,798)	(27,037)
FDIC insurance premium									2,507	3,318	0
Impact of the Tax Act									0	(2,274)	15,441
Addition to reserve for uncertainties									31,123	0	0
Other, net									1,255	641	736
Income tax expense	$ 36,967	$ 25,307	$ 27,532	$ 57,196	$ 18,074	$ 18,046	$ 18,961	$ 13,184	$ 147,002	$ 68,265	$ 90,831