Securities - Amortized Cost and Estimated Fair Value of Investment Securities by Contractual Maturity (Detail) $ in Thousands	Sep. 30, 2019 USD ($)
Amortized Cost
Less than one year, Amortized Cost	$ 71,705
Due after one year through five years, Amortized Cost	190,181
Due after five years through ten years, Amortized Cost	75,453
Due after ten years, Amortized Cost	13,801
Total Amortized Cost	351,140
Estimated Fair Value
Less than one year, Estimated Fair Value	71,726
Due after one year through five years, Estimated Fair Value	192,486
Due after five years through ten years, Estimated Fair Value	72,747
Due after ten years, Estimated Fair Value	14,117
Total Estimated Fair Value	$ 351,076