Investment Securities - Additional Information (Detail) (USD $)	12 Months Ended			12 Months Ended		12 Months Ended
	Dec. 31, 2012	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013 Non-agency CMOs	Mar. 31, 2012 14 non-agency CMOs	Mar. 31, 2013 Maximum	Mar. 31, 2013 Minimum
Schedule of Available-for-sale Securities [Line Items]
Estimated expected cash flows after credit losses						7.00%	4.00%
Number of individual securities		15	20
The discount rates used to establish the net present value of expected cash flows for purposes of determining OTTI ranged from						7.00%	4.00%
The month 1 to month 24 constant default rate						11.50%	4.46%
Six non-agency CMOs with a fair value				$ 6,900,000
Six non-agency CMOs with adjusted cost basis				7,300,000
14 non-agency CMOs with a fair value					19,600,000
14 non-agency CMOs with adjusted cost basis					23,100,000
Unrealized other-than-temporary impairment due to credit losses	558,000			412,000
Realized losses related to credit issues (i.e. principal reduced without a receipt of cash)	364,000			722,000
Unrealized losses on U.S. government sponsored and federal agency obligations, corporate stocks and bonds and Ginnie Mae ("GNMA") mortgage-backed securities as of June 30, 2012 due to changes in interest rates and other non-credit related factors totaled		373,000	291,000
Investment securities available-for-sale with a fair value		$ 187,200,000	$ 216,300,000