Securities - Amortized Cost and Estimated Fair Value of Investment Securities by Contractual Maturity (Detail) $ in Thousands	Mar. 31, 2017 USD ($)
Investments, Debt and Equity Securities [Abstract]
Less than one year, Amortized Cost	$ 14,026
Due after one year through five years, Amortized Cost	118,831
Due after five years through ten years, Amortized Cost	61,459
Due after ten years, Amortized Cost	30,000
Total Amortized Cost	224,316
Less than one year, Estimated Fair Value	14,020
Due after one year through five years, Estimated Fair Value	118,606
Due after five years through ten years, Estimated Fair Value	58,813
Due after ten years, Estimated Fair Value	26,550
Total Estimated Fair Value	$ 217,989