Condensed Parent Company Financial Statements - Summary of Cash Flow of Parent Company (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 99,586	$ 134,879	$ 125,814
Adjustments to reconcile to net cash provided by operating activities:
Amortization of stock-based compensation arrangements of subsidiaries	1,516	1,277	1,352
Other, net	7,305	6,740	(1,199)
Net cash provided by operating activities	154,341	158,958	140,010
INVESTING ACTIVITIES
Other, net	7,820	7,867	(3,890)
Net cash (used in) provided by investing activities	(897,993)	50,347	(293,799)
FINANCING ACTIVITIES
Common stock acquired	(3,098)	(1,601)	(7,914)
Cash dividends paid	(42,472)	(39,805)	(30,265)
Redemption of Junior Subordinated debentures			(5,155)
Net cash provided by (used in) financing activities	492,283	234,721	(179,831)
Net (decrease)/increase in cash, due from banks and interest-bearing deposits	(251,369)	444,026	(333,620)
Cash, due from banks and interest-bearing deposits at the beginning of the period	1,868,281	1,424,255	1,757,875
Cash, due from banks and interest-bearing deposits at the end of the period	1,616,912	1,868,281	1,424,255
SUPPLEMENTAL DISCLOSURE
Cash paid during the period for interest	22,056	54,602	41,549
Cash received during the period for income taxes, net	26,525	30,975	27,952
Parent Company [Member]
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	99,586	134,879	125,814
Adjustments to reconcile to net cash provided by operating activities:
Equity in undistributed earnings of subsidiaries	(51,955)	(61,194)	(87,404)
Amortization of stock-based compensation arrangements of subsidiaries	1,456	1,224	1,306
Other, net	188	(440)	(2,621)
Net cash provided by operating activities	49,275	74,469	37,095
INVESTING ACTIVITIES
Net cash provided by acquisitions			41,347
Payments for investments in subsidiaries	(1,000)	(134,457)
Other, net	(1,175)	(418)	(174)
Net cash (used in) provided by investing activities	(2,175)	(134,875)	41,173
FINANCING ACTIVITIES
Issuance of common stock	1,790	2,484	2,238
Common stock acquired	(3,098)	(1,601)	(7,914)
Cash dividends paid	(42,472)	(39,805)	(30,265)
Redemption of Junior Subordinated debentures			(5,155)
Net cash provided by (used in) financing activities	(43,780)	(38,922)	(41,096)
Net (decrease)/increase in cash, due from banks and interest-bearing deposits	3,320	(99,328)	37,172
Cash, due from banks and interest-bearing deposits at the beginning of the period	5,761	105,089	67,917
Cash, due from banks and interest-bearing deposits at the end of the period	9,081	5,761	105,089
SUPPLEMENTAL DISCLOSURE
Cash paid during the period for interest	1,966	5,131	2,171
Cash received during the period for income taxes, net	$ 2,812	$ 4,518	$ 3,647