Mortgage-backed Securities (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Mar. 31, 2012
Mortgage-backed securities held to maturity pledged as collateral, Amortized Cost	$ 65,000	$ 69,000
Mortgage-backed securities held to maturity pledged as collateral, Fair Value	68,000	71,000
Available-for-sale mortgage-backed securities pledged as collateral, Amortized Cost	544,000	744,000
Available-for-sale mortgage-backed securities pledged as collateral, Fair Value	$ 569,000	$ 776,000