Condensed Parent Company Financial Statements - Schedule of Condensed Income Statement (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
Condensed Income Statements, Captions [Line Items]
Income from securities									$ 484,253	$ 414,957	$ 332,424
Other income									14,355	9,606	8,641
Interest expense									84,349	67,721	42,129
Other expense									62,656	50,721	45,330
Total non-interest expense	$ 92,556	$ 73,268	$ 71,952	$ 74,432	$ 70,990	$ 76,120	$ 63,543	$ 54,571	312,208	265,224	220,860
Provision for income taxes	7,046	8,334	10,103	8,858	10,556	6,516	7,335	7,004	34,341	31,412	53,807
NET INCOME	$ 36,376	$ 37,347	$ 44,814	$ 40,337	$ 43,928	$ 32,486	$ 33,169	$ 33,529	158,873	143,112	94,482
Parent Company [Member]
Condensed Income Statements, Captions [Line Items]
Dividends from subsidiaries—Bank									102,000	86,000	72,000
Dividends from subsidiaries—Nonbank									4,471	486	2,520
Income from securities									15	24	73
Other income									1,433	900	203
Total income									107,919	87,410	74,796
Interest expense									7,660	7,551	6,032
Other expense									8,807	7,940	4,004
Total non-interest expense									16,467	15,491	10,036
Income before income tax benefit and undistributed net income of subsidiaries									91,452	71,919	64,760
Provision for income taxes									(3,207)	(3,739)	(4,726)
Income before undistributed net income of subsidiaries									94,659	75,658	69,486
Equity in undistributed net income of subsidiaries									64,214	67,454	24,996
NET INCOME									$ 158,873	$ 143,112	$ 94,482