Loans and Allowance for Loan Losses - Schedule of Activity in Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 50,381	$ 49,808
Charge-offs	(2,685)	(3,239)
Recoveries	2,305	2,918
Provision	380	347
Ending balance	50,381	49,834
Commercial Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	19,246	21,481
Charge-offs	(245)	(470)
Recoveries	511	603
Provision	79	494
Ending balance	19,591	22,108
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	21,436	18,173
Charge-offs	(3)	(568)
Recoveries	484	1,225
Provision	(1,121)	(877)
Ending balance	20,796	17,953
Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,763	1,643
Charge-offs	(362)	(414)
Recoveries	148	79
Provision	214	428
Ending balance	1,763	1,736
Consumer Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	7,936	8,511
Charge-offs	(2,075)	(1,787)
Recoveries	1,162	1,011
Provision	1,208	302
Ending balance	$ 8,231	$ 8,037