Impaired Loans by Portfolio (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Financing Receivable, Impaired [Line Items]
Average impaired loans for the period	$ 39,843	$ 57,438
Contractual interest income due on impaired loans during the period	2,292	4,433
Interest income on impaired loans recognized on a cash basis	1,694	1,121
Interest income on impaired loans recognized on an accrual basis	332	560
Commercial
Financing Receivable, Impaired [Line Items]
Average impaired loans for the period	7,539	8,659
Contractual interest income due on impaired loans during the period	481	527
Interest income on impaired loans recognized on a cash basis	250	121
Interest income on impaired loans recognized on an accrual basis	117	257
All Other
Financing Receivable, Impaired [Line Items]
Average impaired loans for the period	6,474	6,499
Contractual interest income due on impaired loans during the period	213	112
Interest income on impaired loans recognized on a cash basis	91	82
Interest income on impaired loans recognized on an accrual basis	134	201
Commercial Real Estate Portfolio Segment | Commercial Acquisition, Development and Construction
Financing Receivable, Impaired [Line Items]
Average impaired loans for the period	5,782	12,270
Contractual interest income due on impaired loans during the period	590	1,222
Interest income on impaired loans recognized on a cash basis	269	323
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	11,343	13,838
Contractual interest income due on impaired loans during the period	430	1,181
Interest income on impaired loans recognized on a cash basis	74	175
Interest income on impaired loans recognized on an accrual basis	23	0
Commercial Real Estate Portfolio Segment | Commercial Owner Occupied Real Estate
Financing Receivable, Impaired [Line Items]
Average impaired loans for the period	8,705	16,172
Contractual interest income due on impaired loans during the period	578	1,391
Interest income on impaired loans recognized on a cash basis	1,010	420
Interest income on impaired loans recognized on an accrual basis	$ 58	$ 102