Impaired Loans by Portfolio (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2012	Dec. 31, 2011
Financing Receivable, Impaired [Line Items]
Average impaired loans for the period	$ 62,336	$ 68,377
Contractual interest income due on impaired loans during the period	2,511	4,973
Interest income on impaired loans recognized on a cash basis	666	1,523
Interest income on impaired loans recognized on an accrual basis	224	325
Commercial Loan
Financing Receivable, Impaired [Line Items]
Average impaired loans for the period	8,630	9,800
Contractual interest income due on impaired loans during the period	276	583
Interest income on impaired loans recognized on a cash basis	108	267
Interest income on impaired loans recognized on an accrual basis	73	114
All Other
Financing Receivable, Impaired [Line Items]
Average impaired loans for the period	6,546	6,221
Contractual interest income due on impaired loans during the period	162	1,017
Interest income on impaired loans recognized on a cash basis	18	205
Interest income on impaired loans recognized on an accrual basis	99	166
Commercial Real Estate Portfolio Segment | Commercial Acquisition, Development and Construction
Financing Receivable, Impaired [Line Items]
Average impaired loans for the period	15,353	27,005
Contractual interest income due on impaired loans during the period	687	1,743
Interest income on impaired loans recognized on a cash basis	203	487
Commercial Real Estate Portfolio Segment | Commercial Investor Real Estate
Financing Receivable, Impaired [Line Items]
Average impaired loans for the period	15,000	11,409
Contractual interest income due on impaired loans during the period	653	830
Interest income on impaired loans recognized on a cash basis	48	93
Commercial Real Estate Portfolio Segment | Commercial Owner Occupied Real Estate
Financing Receivable, Impaired [Line Items]
Average impaired loans for the period	16,806	13,942
Contractual interest income due on impaired loans during the period	733	800
Interest income on impaired loans recognized on a cash basis	289	471
Interest income on impaired loans recognized on an accrual basis	$ 52	$ 45