Income Taxes - Reconciliation From Statutory Rate to Effective Tax (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]
Tax expense at statutory rates									$ 30,889	$ 30,223	$ 49,167
Increase (decrease) in taxes resulting from:
State tax, net of federal income tax benefit									8,197	1,002	2,185
Tax-exempt interest income									(3,082)	(2,839)	(5,097)
Bank-owned life insurance									(1,322)	(1,158)	(2,343)
Enactment of Tax Act									0	0	3,912
Other, net									(227)	(1,698)	(1,296)
Income tax expense (benefit)	$ 8,026	$ 9,938	$ 8,802	$ 7,689	$ 6,026	$ 8,575	$ 4,568	$ 6,361	$ 34,455	$ 25,530	$ 46,528