Other Borrowings - Summary of Balances of Other Borrowings (Detail) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Total other borrowings	$ 122,166,000	$ 17,493,000
1.38% Fixed Rate FHLB Collateralized Borrowings [Member]
Debt Instrument [Line Items]
Collateralized borrowing, fixed rate, as of December 31, 2017 of 1.38% & 0.05%, payable on January 2, 2018	104,729,000
0.05% Fixed Rate Collateralized Borrowings [Member]
Debt Instrument [Line Items]
Collateralized borrowing, fixed rate, as of December 31, 2017 of 1.38% & 0.05%, payable on January 2, 2018	$ 17,437,000	$ 17,493,000