Loans, Leases and Other Real Estate - Allowance for Loan and Lease Losses by Portfolio Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Beginning Balance	$ 32,823	$ 30,667	$ 31,245	$ 30,874
Charge-offs	(869)	(1,273)	(3,099)	(3,861)
Recoveries	144	212	907	508
Provision	1,827	1,763	4,872	3,848
Ending Balance	33,925	31,369	33,925	31,369
Ending Balance: Individually evaluated for impairment					$ 21,590	$ 25,285
Ending Balance: Collectively evaluated for impairment					4,070,581	3,847,202
Total Loans and Leases					4,092,893	3,873,895
Ending Balance: Individually evaluated for impairment					504	529
Ending Balance: Collectively evaluated for impairment					33,421	30,716
Ending Balance	32,823	30,667	33,925	31,369	33,925	31,245
Loans Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Ending Balance: Loans acquired with deteriorated credit quality					722	1,408
Commercial, Secured by Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Beginning Balance	23,344	20,359	21,223	20,223
Charge-offs	(315)	(119)	(618)	(393)
Recoveries	26	131	390	212
Provision	1,673	996	3,733	1,325
Ending Balance	24,728	21,367	24,728	21,367
Total Loans and Leases					2,776,899	2,556,601
Ending Balance: Individually evaluated for impairment					480	392
Ending Balance: Collectively evaluated for impairment					24,248	20,831
Ending Balance	23,344	20,359	24,728	21,367	24,728	21,223
Commercial, Secured by Real Estate [Member] | Loans and Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Ending Balance: Individually evaluated for impairment					16,277	18,624
Ending Balance: Collectively evaluated for impairment					2,759,905	2,536,858
Total Loans and Leases					2,776,899	2,556,601
Commercial, Secured by Real Estate [Member] | Loans and Leases [Member] | Loans Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Ending Balance: Loans acquired with deteriorated credit quality					717	1,119
Commercial, Industrial and Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Beginning Balance	1,688	2,212	1,723	2,637
Charge-offs	(196)		(430)	(796)
Recoveries	28	30	150	106
Provision	572	(327)	649	(32)
Ending Balance	2,092	1,915	2,092	1,915
Total Loans and Leases					342,775	350,228
Ending Balance: Individually evaluated for impairment					10	12
Ending Balance: Collectively evaluated for impairment					2,082	1,711
Ending Balance	1,688	2,212	2,092	1,915	2,092	1,723
Commercial, Industrial and Other [Member] | Loans and Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Ending Balance: Individually evaluated for impairment					804	952
Ending Balance: Collectively evaluated for impairment					341,970	349,001
Total Loans and Leases					342,775	350,228
Commercial, Industrial and Other [Member] | Loans and Leases [Member] | Loans Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Ending Balance: Loans acquired with deteriorated credit quality					1	275
Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Beginning Balance	529	624	548	460
Charge-offs	(87)	(44)	(250)	(319)
Recoveries	7	4	39	26
Provision	65	12	177	429
Ending Balance	514	596	514	596
Total Loans and Leases					71,698	67,016
Ending Balance: Collectively evaluated for impairment					514	548
Ending Balance	529	624	514	596	514	548
Leases [Member] | Loans and Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Ending Balance: Collectively evaluated for impairment					71,698	67,016
Total Loans and Leases					71,698	67,016
Real Estate - Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Beginning Balance	1,754	2,164	1,964	2,588
Charge-offs	(98)	(386)	(408)	(692)
Recoveries	3	1	3	5
Provision	(90)	282	10	160
Ending Balance	1,569	2,061	1,569	2,061
Total Loans and Leases					329,625	349,581
Ending Balance: Individually evaluated for impairment					5	31
Ending Balance: Collectively evaluated for impairment					1,564	1,933
Ending Balance	1,754	2,164	1,569	2,061	1,569	1,964
Real Estate - Residential Mortgage [Member] | Loans and Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Ending Balance: Individually evaluated for impairment					1,959	2,911
Ending Balance: Collectively evaluated for impairment					327,666	346,670
Total Loans and Leases					329,625	349,581
Real Estate-Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Beginning Balance	2,596	1,788	2,352	1,591
Charge-offs			(609)
Recoveries	4		24
Provision	(135)	236	698	433
Ending Balance	2,465	2,024	2,465	2,024
Total Loans and Leases					241,207	211,109
Ending Balance: Collectively evaluated for impairment					2,465	2,352
Ending Balance	2,596	1,788	2,465	2,024	2,465	2,352
Real Estate-Construction [Member] | Loans and Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Ending Balance: Individually evaluated for impairment					1,472	1,471
Ending Balance: Collectively evaluated for impairment					239,735	209,638
Total Loans and Leases					241,207	211,109
Home Equity and Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Beginning Balance	2,912	3,520	3,435	3,375
Charge-offs	(173)	(724)	(784)	(1,661)
Recoveries	76	46	301	159
Provision	(258)	564	(395)	1,533
Ending Balance	2,557	3,406	2,557	3,406
Ending Balance: Individually evaluated for impairment					1,078	1,327
Ending Balance: Collectively evaluated for impairment					329,607	338,019
Total Loans and Leases					330,689	339,360
Ending Balance: Individually evaluated for impairment					9	94
Ending Balance: Collectively evaluated for impairment					2,548	3,341
Ending Balance	$ 2,912	$ 3,520	$ 2,557	$ 3,406	2,557	3,435
Home Equity and Consumer [Member] | Loans Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Ending Balance: Loans acquired with deteriorated credit quality					$ 4	$ 14