Noninterest Income and Expense - Components of Noninterest Expense (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Base salaries, net of deferred loan origination costs									$ 62,422	$ 54,589	$ 53,169
Incentive compensation									11,147	9,227	8,872
Benefits and other compensation costs									20,373	19,114	18,683
Total salaries and benefits expense									93,942	82,930	80,724
Occupancy									12,139	10,894	10,139
Data processing and software									11,021	10,448	8,846
Equipment									6,651	7,141	6,597
ATM and POS network charges									5,271	4,752	4,999
Merger and acquisition expense									5,227	530	784
Advertising									4,578	4,101	3,829
Professional fees									3,546	3,745	5,409
Intangible amortization									3,499	1,389	1,377
Telecommunications									3,023	2,713	2,749
Regulatory assessments and insurance									1,906	1,676	2,105
Courier service									1,287	1,035	998
Operational losses									1,260	1,394	1,564
Postage									1,154	1,296	1,603
Legal settlement											1,450
Foreclosed assets expense									382	231	266
Provision for foreclosed asset losses									89	162	140
Other miscellaneous expense									13,720	12,587	12,418
Total other noninterest expense									74,753	64,094	65,273
Total noninterest expense	$ 45,285	$ 47,378	$ 37,870	$ 38,162	$ 38,076	$ 37,222	$ 35,904	$ 35,822	$ 168,695	$ 147,024	$ 145,997