Income Taxes - Summary of Income Tax Reconciliation (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Federal income tax at expected statutory rate									$ 81,683	$ 44,413	$ 51,532
State income tax expense, net of federal tax effect									19,197	15,274	12,866
Tax-exempt interest, net of interest incurred to carry tax-exempt securities									(5,308)	(4,864)	(4,406)
Bank owned life insurance									(2,343)	(2,385)	(2,237)
Tax credits from securities and other investments									(25,954)	(28,988)	(20,555)
Reduction in reserve for uncertainties									0	0	(6,971)
Other, net									(2,041)	488	833
Income tax expense	$ 18,336	$ 17,049	$ 15,460	$ 14,389	$ (10,987)	$ 10,179	$ 12,474	$ 12,272	$ 65,234	$ 23,938	$ 31,062