Investment Securities (Detail) - Investment grades CMO securities (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Fair Value	$ 121,111		$ 140,155
Unrealized Loss	5,524		7,307
OTTI Credit Portion	268	69
OTTI Total	268	69
Collateralized Mortgage Obligations [Member] | Moody/S&P, AAA Rating [Member]
Number of securities	0
Fair Value	0
Unrealized Loss	0
OTTI Credit Portion	0
OTTI Other	0
OTTI Total	0
Collateralized Mortgage Obligations [Member] | Moody/S&P, Aa Rating [Member]
Number of securities	1
Fair Value	11,010
Unrealized Loss	36
OTTI Credit Portion	0
OTTI Other	0
OTTI Total	0
Collateralized Mortgage Obligations [Member] | Moody/S&P A Rating [Member]
Number of securities	6
Fair Value	15,068
Unrealized Loss	372
OTTI Credit Portion	0
OTTI Other	0
OTTI Total	0
Collateralized Mortgage Obligations [Member] | Moody/S&P, BBB Rating [Member]
Number of securities	8
Fair Value	18,068
Unrealized Loss	458
OTTI Credit Portion	0
OTTI Other	0
OTTI Total	0
Collateralized Mortgage Obligations [Member] | Below Investment Grade [Member]
Number of securities	11
Fair Value	40,414
Unrealized Loss	1,473
OTTI Credit Portion	268
OTTI Other	0
OTTI Total	268
Collateralized Mortgage Obligations [Member]
Number of securities	26
Fair Value	84,560		102,918
Unrealized Loss	2,339		3,900
OTTI Credit Portion	268
OTTI Other	0
OTTI Total	$ 268