Debt and Equity Securities - Maturity of Amortized Cost and Estimated Market Value of Debt Securities (Detail) $ in Thousands	Mar. 31, 2016 USD ($)
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities, Due in one year or less, Amortized Cost	$ 1,909
Available-for-sale securities, Due after one year through five years, Amortized Cost	9,638
Available-for-sale securities, Due after five years through ten years, Amortized Cost	4,765
Available-for-sale securities, Due after ten years, Amortized Cost	13,650
Available-for-sale securities, Gross Amortized Cost	29,962
Available-for-sale securities, Due in one year or less, Estimated Market Value	1,918
Available-for-sale securities, Due after one year through five years, Estimated Market Value	9,769
Available-for-sale securities, Due after five years through ten years, Estimated Market Value	4,840
Available-for-sale securities, Due after ten years, Estimated Market Value	13,705
Available-for-sale securities, Gross Estimated Market Value	30,232
Held-to-maturity, Due in one year or less, Amortized Cost	0
Held-to-maturity, Due after one year through five years, Amortized Cost	45,642
Held-to-maturity, Due after five years through ten years, Amortized Cost	93,629
Held-to-maturity, Due after ten years, Amortized Cost	167,700
Held-to-maturity, Gross Amortized Cost	306,971
Held-to-maturity, Due in one year or less, Estimated Market Value	0
Held-to-maturity, Due after one year through five years, Estimated Market Value	45,971
Held-to-maturity, Due after five years through ten years, Estimated Market Value	94,283
Held-to-maturity, Due after ten years, Estimated Market Value	168,105
Held-to-maturity, Gross Estimated Market Value	$ 308,359