Business Combinations - Schedule of Business Acquisition Pro-forma Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Summarized proforma income statement data:
Net interest income	$ 242,793	$ 227,795
(Provision for) benefit from loan losses	(2,180)	271
Noninterest income	51,152	53,881
Noninterest expense	(180,884)	(181,833)
Income before taxes	110,881	100,114
Income taxes	(30,337)	(47,352)
Net income	$ 80,544	$ 52,762
Basic earnings per share (in USD per share)	$ 2.65	$ 1.74
Diluted earnings per share (in USD per share)	$ 2.63	$ 1.72