Securities - Amortized Cost and Estimated Fair Value of Investment Securities by Contractual Maturity (Detail) $ in Thousands	Jun. 30, 2017 USD ($)
Investments, Debt and Equity Securities [Abstract]
Less than one year, Amortized Cost	$ 28,955
Due after one year through five years, Amortized Cost	132,163
Due after five years through ten years, Amortized Cost	76,375
Due after ten years, Amortized Cost	30,000
Total Amortized Cost	267,493
Less than one year, Estimated Fair Value	28,936
Due after one year through five years, Estimated Fair Value	132,089
Due after five years through ten years, Estimated Fair Value	75,343
Due after ten years, Estimated Fair Value	27,669
Total Estimated Fair Value	$ 264,037