Noninterest Income and Expense - Components of Noninterest Expense (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
Other Income and Expenses [Abstract]
Base salaries, net of deferred loan origination costs									$ 70,218	$ 62,422	$ 54,589
Incentive compensation									13,106	11,147	9,227
Benefits and other compensation costs									22,741	20,373	19,114
Total salaries and benefits expense									106,065	93,942	82,930
Occupancy									14,893	12,139	10,894
Data processing and software									13,517	11,021	10,448
Equipment									7,022	6,651	7,141
ATM and POS network charges									5,447	5,271	4,752
Merger and acquisition expense									0	5,227	530
Advertising									5,633	4,578	4,101
Professional fees									3,754	3,546	3,745
Intangible amortization									5,723	3,499	1,389
Telecommunications									3,190	3,023	2,713
Regulatory assessments and insurance									1,188	1,906	1,676
Courier service									1,308	1,287	1,035
Operational losses									986	1,260	1,394
Postage									1,258	1,154	1,296
Gain on sale of real estate owned									(246)	(408)	(711)
Loss on disposal of fixed assets									82	185	142
Other miscellaneous expense									15,637	14,191	12,980
Total other noninterest expense									79,392	74,530	63,525
Total noninterest expense	$ 46,964	$ 46,344	$ 46,697	$ 45,452	$ 45,285	$ 47,378	$ 37,870	$ 38,162	$ 185,457	$ 168,472	$ 146,455