Loans and Allowance for Loan Losses - Schedule of Activity in Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 50,381	$ 49,834	$ 50,381	$ 49,808
Charge-offs	(3,054)	(3,380)	(5,739)	(6,619)
Recoveries	3,887	3,177	6,192	6,095
Provision	2,446	1,355	2,826	1,702
Ending balance	53,660	50,986	53,660	50,986
Commercial Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	19,591	22,108	19,246	21,481
Charge-offs	(472)	(411)	(717)	(881)
Recoveries	249	789	760	1,392
Provision	2,019	(2,121)	2,098	(1,627)
Ending balance	21,387	20,365	21,387	20,365
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	20,796	17,953	21,436	18,173
Charge-offs	(430)	(1,068)	(433)	(1,636)
Recoveries	583	1,522	1,067	2,747
Provision	1,549	2,247	428	1,370
Ending balance	22,498	20,654	22,498	20,654
Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,763	1,736	1,763	1,643
Charge-offs	(295)	(313)	(657)	(727)
Recoveries	1,697	28	1,845	107
Provision	(1,298)	360	(1,084)	788
Ending balance	1,867	1,811	1,867	1,811
Consumer Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	8,231	8,037	7,936	8,511
Charge-offs	(1,857)	(1,588)	(3,932)	(3,375)
Recoveries	1,358	838	2,520	1,849
Provision	176	869	1,384	1,171
Ending balance	$ 7,908	$ 8,156	$ 7,908	$ 8,156