Securities - Schedule of Contractual Maturity of Securities Available for Sale, Excluding Equity Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Amortized Cost
1 year or less	$ 58,770
1 year – 5 years	131,226
5 years – 10 years	65,503
After 10 years	5,521
Total, Amortized Cost	261,020
Total debt securities	498,814	$ 521,337
Fair Value
1 year or less	58,412
1 year – 5 years	131,749
5 years – 10 years	67,547
After 10 years	5,661
Total, Fair Value	263,369
Total debt securities	500,608	516,863
Residential and multi-family mortgage
Amortized Cost
Mortgage & asset backed securities, Amortized Cost	207,588
Fair Value
Mortgage & asset backed securities, Fair Value	207,491
Pooled SBA
Amortized Cost
Mortgage & asset backed securities, Amortized Cost	29,186
Total debt securities	29,186	30,163
Fair Value
Mortgage & asset backed securities, Fair Value	28,801
Total debt securities	28,801	29,374
Other
Amortized Cost
Mortgage & asset backed securities, Amortized Cost	1,020
Total debt securities	1,020	1,020
Fair Value
Mortgage & asset backed securities, Fair Value	947
Total debt securities	$ 947	$ 934