Securities - Schedule of Contractual Maturity of Securities Available for Sale, Excluding Equity Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Amortized Cost
1 year or less	$ 58,509
1 year – 5 years	146,605
5 years – 10 years	70,984
After 10 years	4,930
Total, Amortized Cost	281,028
Amortized cost	521,337	$ 409,110
Fair Value
1 year or less	58,003
1 year – 5 years	146,111
5 years – 10 years	71,451
After 10 years	4,937
Total, Fair Value	280,502
Securities available for sale	516,863	409,709
Residential & multi-family mortgage
Amortized Cost
Mortgage & asset backed securities, Amortized Cost	209,126
Amortized cost	209,126	111,214
Fair Value
Mortgage & asset backed securities, Fair Value	206,053
Securities available for sale	206,053	109,636
Pooled SBA
Amortized Cost
Mortgage & asset backed securities, Amortized Cost	30,163
Amortized cost	30,163	36,260
Fair Value
Mortgage & asset backed securities, Fair Value	29,374
Securities available for sale	29,374	36,040
Other
Amortized Cost
Mortgage & asset backed securities, Amortized Cost	1,020
Amortized cost	1,020	1,020
Fair Value
Mortgage & asset backed securities, Fair Value	934
Securities available for sale	$ 934	$ 962