Condensed Parent Company Financial Statements - Schedule of Condensed Income 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
Condensed Income Statements, Captions [Line Items]
Income from securities									$ 541,277	$ 484,253	$ 414,957
Other income									21,728	14,355	9,606
Interest expense									61,797	84,349	67,721
Other expense									70,748	62,656	50,721
Total non-interest expense	$ 88,069	$ 89,943	$ 85,502	$ 91,333	$ 92,556	$ 73,268	$ 71,952	$ 74,432	354,845	312,208	265,224
Provision for income taxes	11,703	7,669	42	3,621	7,046	8,334	10,103	8,858	23,035	34,341	31,412
NET INCOME	52,854	41,305	4,488	23,396	$ 36,376	$ 37,347	$ 44,814	$ 40,337	122,044	158,873	143,112
Preferred stock dividends	2,644								2,644
NET INCOME AVAILABLE TO COMMON SHAREHOLDERS	$ 50,210	$ 41,305	$ 4,488	$ 23,396					119,400	158,873	143,112
Parent Company [Member]
Condensed Income Statements, Captions [Line Items]
Dividends from subsidiaries—Bank									64,000	102,000	86,000
Dividends from subsidiaries—Nonbank									1,200	4,471	486
Income from securities									(22)	15	24
Other income									485	1,433	900
Total income									65,663	107,919	87,410
Interest expense									6,964	7,660	7,551
Other expense									5,415	8,807	7,940
Total non-interest expense									12,379	16,467	15,491
Income before income tax benefit and undistributed net income of subsidiaries									53,284	91,452	71,919
Provision for income taxes									(2,471)	(3,207)	(3,739)
Income before undistributed net income of subsidiaries									55,755	94,659	75,658
Equity in undistributed net income of subsidiaries									66,289	64,214	67,454
NET INCOME									122,044	158,873	143,112
Preferred stock dividends									2,644
NET INCOME AVAILABLE TO COMMON SHAREHOLDERS									$ 119,400	$ 158,873	$ 143,112