Investments - Additional Information (Detail) (USD $)	3 Months Ended	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2012	Dec. 31, 2011
Investment [Line Items]
Overall default probabilities percentage		0.30%
Recovery and prepayment probabilities percentage		2.00%
Discount rate assumption	12.60%	12.60%
Pooled trust preferred security incurred credit-related other-than-temporary impairment ("OTTI")	$ 8,000	$ 72,000
Cumulative credit-related OTTI	72,000	72,000	422,000
Non-credit related OTTI recognized in other comprehensive income ("OCI")		400,000
Investments available-for-sale book value	221,200,000	221,200,000	255,400,000
Investments held-to-maturity book value	130,300,000	130,300,000	58,700,000
Financial Institutions
Investment [Line Items]
Trust preferred portfolio Fair Value	1,500,000	1,500,000
Banks and Financial Institutions
Investment [Line Items]
Trust preferred portfolio Fair Value	1,800,000	1,800,000
Trust preferred portfolio	2,200,000	2,200,000
Government National Mortgage Association Certificates and Obligations (GNMA)
Investment [Line Items]
Mortgage-backed portfolio	208,500,000	208,500,000
Government National Mortgage Association Certificates and Obligations (GNMA) | Federal Home Loan Mortgage and Federal National Mortgage Association | Federal Home Loan Mortgage Corporation
Investment [Line Items]
Mortgage-backed portfolio	$ 301,000,000	$ 301,000,000