Loans and Allowance for Loan Losses - Schedule of Activity in Allowance for Loan Losses (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 53,660	$ 50,986	$ 50,381	$ 49,808
Charge-offs	(4,261)	(2,821)	(10,000)	(9,440)
Recoveries	2,564	1,693	8,756	7,788
Provision	750	311	3,576	2,013
Ending balance	52,713	50,169	52,713	50,169
Commercial Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	21,387	20,365	19,246	21,481
Charge-offs	(1,662)	(70)	(2,378)	(951)
Recoveries	467	255	1,227	1,647
Provision	(473)	(23)	1,624	(1,650)
Ending balance	19,719	20,527	19,719	20,527
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	22,498	20,654	21,436	18,173
Charge-offs	(241)	(1,148)	(675)	(2,784)
Recoveries	944	339	2,011	3,086
Provision	(309)	180	120	1,550
Ending balance	22,892	20,025	22,892	20,025
Residential [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	1,867	1,811	1,763	1,643
Charge-offs	(284)	(227)	(941)	(954)
Recoveries	45	89	1,890	196
Provision	292	236	(792)	1,024
Ending balance	1,920	1,909	1,920	1,909
Consumer Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	7,908	8,156	7,936	8,511
Charge-offs	(2,074)	(1,376)	(6,006)	(4,751)
Recoveries	1,108	1,010	3,628	2,859
Provision	1,240	(82)	2,624	1,089
Ending balance	$ 8,182	$ 7,708	$ 8,182	$ 7,708