Investment Securities - Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012
Investments Debt And Equity Securities [Abstract]
Due in one year, Amortized Cost	$ 505
Due after one year through five years, Amortized Cost	3,819
Due after five years through ten years, Amortized Cost	33,017
Due after ten years, Amortized Cost	63,104
Totals, Amortized Cost	100,445
Due in one year, Amortized Cost, Held to Maturity
Due after one year through five years, Amortized Cost, Held to Maturity
Due after five years through ten years, Amortized Cost, Held to Maturity
Due after ten years, Amortized Cost, Held to Maturity	240,504
Totals, Amortized Cost, Held to Maturity	240,504	0	0
Due in one year, Estimated Fair Value	536
Due after one year through five years, Estimated Fair Value	3,966
Due after five years through ten years, Estimated Fair Value	33,988
Due after ten years, Estimated Fair Value	66,157
Totals, Estimated Fair Value	104,647
Due in one year, Estimated Fair Value, Held to Maturity
Due after one year through five years, Estimated Fair Value, Held to Maturity
Due after five years through ten years, Estimated Fair Value, Held to Maturity
Due after ten years, Estimated Fair Value, Held to Maturity	233,807
Estimated Fair Value, Held to Maturity	$ 233,807		$ 0