Credit Risk Rating Indicators for Each Segment of Commercial Loan Portfolio (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	$ 2,565,069	$ 2,531,128
Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	344,489	346,708
Commercial Portfolio Segment
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	1,548,710	1,527,039
Commercial Portfolio Segment | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	344,489	346,708
Commercial Portfolio Segment | Commercial Acquisition, Development and Construction
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	150,599	151,933
Commercial Portfolio Segment | Commercial Investor Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	487,802	456,888
Commercial Portfolio Segment | Commercial Owner Occupied Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	565,820	571,510
Commercial Portfolio Segment | Pass
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	1,381,796	1,373,442
Commercial Portfolio Segment | Pass | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	293,923	305,348
Commercial Portfolio Segment | Pass | Commercial Acquisition, Development and Construction
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	139,623	141,802
Commercial Portfolio Segment | Pass | Commercial Investor Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	431,166	405,448
Commercial Portfolio Segment | Pass | Commercial Owner Occupied Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	517,084	520,844
Commercial Portfolio Segment | Special Mention
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	53,145	54,621
Commercial Portfolio Segment | Special Mention | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	18,030	13,603
Commercial Portfolio Segment | Special Mention | Commercial Acquisition, Development and Construction
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	374	1,793
Commercial Portfolio Segment | Special Mention | Commercial Investor Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	15,775	21,963
Commercial Portfolio Segment | Special Mention | Commercial Owner Occupied Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	18,966	17,262
Commercial Portfolio Segment | Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	111,220	95,927
Commercial Portfolio Segment | Substandard | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	31,312	26,091
Commercial Portfolio Segment | Substandard | Commercial Acquisition, Development and Construction
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	10,602	8,338
Commercial Portfolio Segment | Substandard | Commercial Investor Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	40,307	28,885
Commercial Portfolio Segment | Substandard | Commercial Owner Occupied Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	28,999	32,613
Commercial Portfolio Segment | Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	2,549	3,049
Commercial Portfolio Segment | Doubtful | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	1,224	1,666
Commercial Portfolio Segment | Doubtful | Commercial Acquisition, Development and Construction
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	0	0
Commercial Portfolio Segment | Doubtful | Commercial Investor Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	554	592
Commercial Portfolio Segment | Doubtful | Commercial Owner Occupied Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	$ 771	$ 791