Credit Quality Assessment (Credit Quality of Loan Portfolio) (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Financing Receivable Recorded Investment Past Due [Line Items]
31-60 days	$ 9,083,000	$ 9,663,000
61-90 days	3,877,000	3,979,000
> 90 days	0	0
Total past due	12,960,000	13,642,000
Non-accrual loans and leases	30,571,000	28,530,000
Loans aquired with deteriorated credit quality	2,925,000	3,011,000
Current loans	3,118,250,000	3,082,209,000
Total loans and leases	3,164,706,000	3,127,392,000
Commercial
Financing Receivable Recorded Investment Past Due [Line Items]
31-60 days	435,000	759,000
61-90 days	0	995,000
> 90 days	0	0
Total past due	435,000	1,754,000
Non-accrual loans and leases	4,166,000	3,184,000
Loans aquired with deteriorated credit quality	1,213,000	1,238,000
Current loans	379,638,000	384,605,000
Total loans and leases	385,452,000	390,781,000
Leases
Financing Receivable Recorded Investment Past Due [Line Items]
31-60 days	3,000	11,000
61-90 days	2,000	0
> 90 days	0	0
Total past due	5,000	11,000
Non-accrual loans and leases	0	0
Loans aquired with deteriorated credit quality	0	0
Current loans	31,000	43,000
Total loans and leases	36,000	54,000
Consumer
Financing Receivable Recorded Investment Past Due [Line Items]
31-60 days	605,000	797,000
61-90 days	266,000	179,000
> 90 days	0	0
Total past due	871,000	976,000
Non-accrual loans and leases	1,962,000	1,668,000
Loans aquired with deteriorated credit quality	0	0
Current loans	425,698,000	422,908,000
Total loans and leases	428,531,000	425,552,000
Commercial Real Estate Portfolio Segment | Commercial Acquisition, Development and Construction
Financing Receivable Recorded Investment Past Due [Line Items]
31-60 days	711,000	0
61-90 days	0	320,000
> 90 days	0	0
Total past due	711,000	320,000
Non-accrual loans and leases	1,363,000	2,464,000
Loans aquired with deteriorated credit quality	0	0
Current loans	201,657,000	202,340,000
Total loans and leases	203,731,000	205,124,000
Commercial Real Estate Portfolio Segment | Commercial Investor Real Estate
Financing Receivable Recorded Investment Past Due [Line Items]
31-60 days	1,352,000	2,374,000
61-90 days	0	1,493,000
> 90 days	0	0
Total past due	1,352,000	3,867,000
Non-accrual loans and leases	10,083,000	8,156,000
Loans aquired with deteriorated credit quality	0	0
Current loans	657,496,000	628,170,000
Total loans and leases	668,931,000	640,193,000
Commercial Real Estate Portfolio Segment | Commercial Owner Occupied Real Estate
Financing Receivable Recorded Investment Past Due [Line Items]
31-60 days	1,373,000	2,658,000
61-90 days	207,000	156,000
> 90 days	0	0
Total past due	1,580,000	2,814,000
Non-accrual loans and leases	8,974,000	8,941,000
Loans aquired with deteriorated credit quality	1,712,000	1,773,000
Current loans	606,580,000	597,533,000
Total loans and leases	618,846,000	611,061,000
Residential Real Estate Portfolio Segment | Residential Mortgage
Financing Receivable Recorded Investment Past Due [Line Items]
31-60 days	4,604,000	3,064,000
61-90 days	3,402,000	836,000
> 90 days	0	0
Total past due	8,006,000	3,900,000
Non-accrual loans and leases	3,235,000	3,012,000
Loans aquired with deteriorated credit quality	0	0
Current loans	717,617,000	710,974,000
Total loans and leases	728,858,000	717,886,000
Residential Real Estate Portfolio Segment | Residential Construction
Financing Receivable Recorded Investment Past Due [Line Items]
31-60 days	0	0
61-90 days	0	0
> 90 days	0	0
Total past due	0	0
Non-accrual loans and leases	788,000	1,105,000
Loans aquired with deteriorated credit quality	0	0
Current loans	129,533,000	135,636,000
Total loans and leases	$ 130,321,000	$ 136,741,000