Impaired Loans by Portfolio (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Financing Receivable, Impaired [Line Items]
Average impaired loans for the period	$ 59,353	$ 68,377
Contractual interest income due on impaired loans during the period	3,168	4,973
Interest income on impaired loans recognized on a cash basis	927	1,523
Interest income on impaired loans recognized on an accrual basis	403	325
Commercial Loan
Financing Receivable, Impaired [Line Items]
Average impaired loans for the period	8,578	9,800
Contractual interest income due on impaired loans during the period	266	583
Interest income on impaired loans recognized on a cash basis	109	267
Interest income on impaired loans recognized on an accrual basis	154	114
Commercial Acquisition, Development and Construction
Financing Receivable, Impaired [Line Items]
Average impaired loans for the period	13,754
Commercial Investor Real Estate
Financing Receivable, Impaired [Line Items]
Average impaired loans for the period	14,336
Commercial Owner Occupied Real Estate
Financing Receivable, Impaired [Line Items]
Average impaired loans for the period	16,419
All Other
Financing Receivable, Impaired [Line Items]
Average impaired loans for the period	6,265	6,221
Contractual interest income due on impaired loans during the period	39	1,017
Interest income on impaired loans recognized on a cash basis	22	205
Interest income on impaired loans recognized on an accrual basis	172	166
Commercial Real Estate Portfolio Segment | Commercial Acquisition, Development and Construction
Financing Receivable, Impaired [Line Items]
Average impaired loans for the period	13,754	27,005
Contractual interest income due on impaired loans during the period	936	1,743
Interest income on impaired loans recognized on a cash basis	268	487
Commercial Real Estate Portfolio Segment | Commercial Investor Real Estate
Financing Receivable, Impaired [Line Items]
Average impaired loans for the period	14,336	11,409
Contractual interest income due on impaired loans during the period	931	830
Interest income on impaired loans recognized on a cash basis	162	93
Commercial Real Estate Portfolio Segment | Commercial Owner Occupied Real Estate
Financing Receivable, Impaired [Line Items]
Average impaired loans for the period	16,419	13,942
Contractual interest income due on impaired loans during the period	996	800
Interest income on impaired loans recognized on a cash basis	366	471
Interest income on impaired loans recognized on an accrual basis	$ 77	$ 45