Securities - Amortized Cost and Estimated Fair Value of Investment Securities by Contractual Maturity (Detail) $ in Thousands	Sep. 30, 2015 USD ($)
Investments, Debt and Equity Securities [Abstract]
Less than one year, Amortized Cost	$ 45,234
Due after one year through five years, Amortized Cost	48,034
Due after five years through ten years, Amortized Cost	340
Due after ten years, Amortized Cost	55,000
Total Amortized Cost	148,608
Less than one year, Estimated Fair Value	45,281
Due after one year through five years, Estimated Fair Value	48,388
Due after five years through ten years, Estimated Fair Value	342
Due after ten years, Estimated Fair Value	48,072
Total Estimated Fair Value	$ 142,083