Debt and Equity Securities - Maturity of Amortized Cost and Estimated Market Value of Debt Securities (Detail) $ in Thousands	Jun. 30, 2015 USD ($)
Debt And Equity Securities [Abstract]
Available-for-sale securities, Due in one year or less, Estimated Market Value	$ 2,777
Available-for-sale securities, Due after one year through five years, Estimated Market Value	9,978
Available-for-sale securities, Due after five years through ten years, Estimated Market Value	3,382
Available-for-sale securities, Due after ten years, Estimated Market Value	10,067
Available-for-sale securities, Gross Estimated Market Value	26,204
Available-for-sale securities, Due in one year or less, Amortized Cost	2,813
Available-for-sale securities, Due after one year through five years, Amortized Cost	10,082
Available-for-sale securities, Due after five years through ten years, Amortized Cost	3,419
Available-for-sale securities, Due after ten years, Amortized Cost	9,937
Available-for-sale securities, Gross Amortized Cost	26,251
Held-to-maturity, Due in one year or less, Estimated Market Value	2,000
Held-to-maturity, Due after one year through five years, Estimated Market Value	46,710
Held-to-maturity, Due after five years through ten years, Estimated Market Value	138,966
Held-to-maturity, Due after ten years, Estimated Market Value	141,979
Held-to-maturity, Gross Estimated Market Value	329,655
Held-to-maturity, Due in one year or less, Amortized Cost	2,001
Held-to-maturity, Due after one year through five years, Amortized Cost	46,724
Held-to-maturity, Due after five years through ten years, Amortized Cost	138,322
Held-to-maturity, Due after ten years, Amortized Cost	141,437
Held-to-maturity, Gross Amortized Cost	$ 328,484