Impaired Loans by Portfolio (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Financing Receivable, Impaired [Line Items]
Average impaired loans for the period	$ 42,761	$ 57,438
Contractual interest income due on impaired loans during the period	1,881	4,433
Interest income on impaired loans recognized on a cash basis	1,677	1,121
Interest income on impaired loans recognized on an accrual basis	221	560
Commercial
Financing Receivable, Impaired [Line Items]
Average impaired loans for the period	7,865	8,659
Contractual interest income due on impaired loans during the period	334	527
Interest income on impaired loans recognized on a cash basis	136	121
Interest income on impaired loans recognized on an accrual basis	66	257
All Other
Financing Receivable, Impaired [Line Items]
Average impaired loans for the period	6,523	6,499
Contractual interest income due on impaired loans during the period	158	112
Interest income on impaired loans recognized on a cash basis	40	82
Interest income on impaired loans recognized on an accrual basis	89	201
Commercial Real Estate Portfolio Segment | Commercial Acquisition, Development and Construction
Financing Receivable, Impaired [Line Items]
Average impaired loans for the period	6,014	12,270
Contractual interest income due on impaired loans during the period	430	1,222
Interest income on impaired loans recognized on a cash basis	185	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	12,547	13,838
Contractual interest income due on impaired loans during the period	515	1,181
Interest income on impaired loans recognized on a cash basis	397	175
Interest income on impaired loans recognized on an accrual basis	15	0
Commercial Real Estate Portfolio Segment | Commercial Owner Occupied Real Estate
Financing Receivable, Impaired [Line Items]
Average impaired loans for the period	9,812	16,172
Contractual interest income due on impaired loans during the period	444	1,391
Interest income on impaired loans recognized on a cash basis	919	420
Interest income on impaired loans recognized on an accrual basis	$ 51	$ 102