Impaired Loans by Portfolio (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Financing Receivable, Impaired [Line Items]
Average impaired loans for the period	$ 57,438	$ 68,377	$ 75,556
Contractual interest income due on impaired loans during the period	4,433	4,973	6,651
Interest income on impaired loans recognized on a cash basis	1,121	1,523	0
Interest income on impaired loans recognized on an accrual basis	560	325	524
Commercial Loan
Financing Receivable, Impaired [Line Items]
Average impaired loans for the period	8,659	9,800
Contractual interest income due on impaired loans during the period	527	583
Interest income on impaired loans recognized on a cash basis	121	267
Interest income on impaired loans recognized on an accrual basis	257	114
All Other
Financing Receivable, Impaired [Line Items]
Average impaired loans for the period	6,499	6,221
Contractual interest income due on impaired loans during the period	112	1,017
Interest income on impaired loans recognized on a cash basis	82	205
Interest income on impaired loans recognized on an accrual basis	201	166
Commercial Real Estate Portfolio Segment | Commercial Acquisition, Development and Construction
Financing Receivable, Impaired [Line Items]
Average impaired loans for the period	12,270	27,005
Contractual interest income due on impaired loans during the period	1,222	1,743
Interest income on impaired loans recognized on a cash basis	323	487
Interest income on impaired loans recognized on an accrual basis	0	0
Commercial Real Estate Portfolio Segment | Commercial Investor Real Estate
Financing Receivable, Impaired [Line Items]
Average impaired loans for the period	13,838	11,409
Contractual interest income due on impaired loans during the period	1,181	830
Interest income on impaired loans recognized on a cash basis	175	93
Interest income on impaired loans recognized on an accrual basis	0	0
Commercial Real Estate Portfolio Segment | Commercial Owner Occupied Real Estate
Financing Receivable, Impaired [Line Items]
Average impaired loans for the period	16,172	13,942
Contractual interest income due on impaired loans during the period	1,391	800
Interest income on impaired loans recognized on a cash basis	420	471
Interest income on impaired loans recognized on an accrual basis	$ 102	$ 45