Debt and Equity Securities - Maturity of Amortized Cost and Estimated Market Value of Debt Securities (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Debt And Equity Securities [Abstract]
Available-for-sale securities, Due in one year or less, Estimated Market Value	$ 3,133
Available-for-sale securities, Due after one year through five years, Estimated Market Value	10,139
Available-for-sale securities, Due after five years through ten years, Estimated Market Value	3,741
Available-for-sale securities, Due after ten years, Estimated Market Value	11,141
Available-for-sale securities, Gross Estimated Market Value	28,154
Available-for-sale securities, Due in one year or less, Amortized Cost	3,165
Available-for-sale securities, Due after one year through five years, Amortized Cost	10,295
Available-for-sale securities, Due after five years through ten years, Amortized Cost	3,769
Available-for-sale securities, Due after ten years, Amortized Cost	11,160
Available-for-sale securities, Gross Amortized Cost	28,389
Held-to-maturity, Due in one year or less, Estimated Market Value		2,001
Held-to-maturity, Due after one year through five years, Estimated Market Value		59,146
Held-to-maturity, Due after five years through ten years, Estimated Market Value		148,273
Held-to-maturity, Due after ten years, Estimated Market Value		126,381
Held-to-maturity, Gross Estimated Market Value		335,801
Held-to-maturity, Due in one year or less, Amortized Cost	2,002
Held-to-maturity, Due after one year through five years, Amortized Cost	59,080
Held-to-maturity, Due after five years through ten years, Amortized Cost	148,496
Held-to-maturity, Due after ten years, Amortized Cost	127,033
Held-to-maturity, Gross Amortized Cost	$ 336,611