Condensed Parent Company Financial Statements - Schedule of Condensed Cash Flow Statement (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
OPERATING ACTIVITIES
Net income	$ 52,854	$ 41,305	$ 4,488	$ 23,396	$ 36,376	$ 37,347	$ 44,814	$ 40,337	$ 122,044	$ 158,873	$ 143,112
Adjustments to reconcile net income to net cash provided by operating activities:
Net change in: accrued interest receivable and other assets									(30,280)	(33,400)	19,895
Net securities (gains) losses									(4,268)	(4,320)	900
Other—net									2,358	(139)	(233)
Net cash provided by operating activities									59,606	163,363	191,891
INVESTING ACTIVITIES
Proceeds from sales—securities available-for-sale									226,099	125,839	82,134
Acquisitions and additional capitalization of subsidiaries, net of cash acquired										60,025	278,654
Net cash provided by (used in) investing activities									57,792	103,786	(51,859)
FINANCING ACTIVITIES
Repayment of junior subordinated debt									(6,702)	(33,506)	(17,519)
Issuance of common stock									59	72	1,578
Issuance of preferred stock									144,484
Treasury shares purchased—net									(24,540)	(10,211)	(426)
Dividends paid to common and preferred shareholders									(85,253)	(66,571)	(53,577)
Net cash provided by (used in) financing activities									553,253	(201,539)	(88,418)
Net increase in cash, cash equivalents and restricted cash									670,651	65,610	51,614
Cash, cash equivalents and restricted cash at beginning of the year				234,796				169,186	234,796	169,186	117,572
Cash, cash equivalents and restricted cash at end of the year	905,447				234,796				905,447	234,796	169,186
Parent Company [Member]
OPERATING ACTIVITIES
Net income									122,044	158,873	143,112
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed net income									(66,289)	(64,214)	(67,454)
Net change in: accrued interest receivable and other assets									121	(5,443)	(3,612)
Net securities (gains) losses									22	(19)	36
Other—net									5,865	6,898	4,988
Net cash provided by operating activities									61,763	96,095	77,070
INVESTING ACTIVITIES
Proceeds from sales—securities available-for-sale									203	1,007	1,511
Acquisitions and additional capitalization of subsidiaries, net of cash acquired									(35,000)	62,112	37,309
Net cash provided by (used in) investing activities									(34,797)	63,119	38,820
FINANCING ACTIVITIES
Repayment of junior subordinated debt									(6,702)	(33,506)	(17,519)
Issuance of common stock									59	72	1,578
Issuance of preferred stock									144,484
Treasury shares purchased—net									(24,540)	(10,211)	(426)
Dividends paid to common and preferred shareholders									(87,897)	(66,572)	(53,577)
Net cash provided by (used in) financing activities									25,404	(110,217)	(69,944)
Net increase in cash, cash equivalents and restricted cash									52,370	48,997	45,946
Cash, cash equivalents and restricted cash at beginning of the year				$ 170,854				$ 121,857	170,854	121,857	75,911
Cash, cash equivalents and restricted cash at end of the year	$ 223,224				$ 170,854				$ 223,224	$ 170,854	$ 121,857