Investment Securities - Summary of Contractual Maturities of Investment Securities Classified as Available for Sale and Held to Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Available for Sale, Amortized Cost
Due in one year or less	$ 29,733
Due after one year through five years	105,745
Due after five years through ten years	52,534
Due after ten years	15,328
Total	203,340
Amortized Cost	752,260	$ 649,741
Available for Sale, Fair Value
Due in one year or less	29,786
Due after one year through five years	106,611
Due after five years through ten years	53,385
Due after ten years	15,054
Total	204,836
Investment securities, available for sale, at fair value	755,900	638,618
Held to Maturity, Amortized Cost
Due in one year or less	7,321
Due after one year through five years	31,102
Due after five years through ten years	6,815
Due after ten years	758
Total	45,996
Amortized Cost	123,975	153,646
Held to Maturity, Fair Value
Due in one year or less	7,328
Due after one year through five years	31,425
Due after five years through ten years	6,852
Due after ten years	760
Total	46,365
Total securities, Held to Maturity, Fair Value	124,904	$ 150,932
Mortgage-backed securities
Available for Sale, Amortized Cost
Available for sale	548,920
Available for Sale, Fair Value
Available for sale	551,064
Held to Maturity, Amortized Cost
Held to maturity	77,979
Held to Maturity, Fair Value
Held to maturity	$ 78,539