Securities - Contractual Maturity (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Amortized Cost
1 year or less	$ 58,844
1 year – 5 years	164,854
5 years – 10 years	70,767
After 10 years	3,775
Total, Amortized Cost	298,240
Total debt securities, Amortized Cost	531,307	$ 409,110
Fair Value
1 year or less	58,554
1 year – 5 years	163,471
5 years – 10 years	70,223
After 10 years	3,692
Total, Fair Value	295,940
Total debt securities, Fair Value	522,334	409,709
Residential & multi-family mortgage
Amortized Cost
Mortgage & asset backed securities, Amortized Cost	199,968
Total debt securities, Amortized Cost	199,968	111,214
Fair Value
Mortgage & asset backed securities, Fair Value	194,635
Total debt securities, Fair Value	194,635	109,636
Pooled SBA
Amortized Cost
Mortgage & asset backed securities, Amortized Cost	32,079
Total debt securities, Amortized Cost	32,079	36,260
Fair Value
Mortgage & asset backed securities, Fair Value	30,833
Total debt securities, Fair Value	30,833	36,040
Other
Amortized Cost
Mortgage & asset backed securities, Amortized Cost	1,020
Total debt securities, Amortized Cost	1,020	1,020
Fair Value
Mortgage & asset backed securities, Fair Value	926
Total debt securities, Fair Value	$ 926	$ 962