Annual report pursuant to Section 13 and 15(d)

Borrowings - Summary of Contractual Maturities Pertaining to FHLB (Detail)

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Borrowings - Summary of Contractual Maturities Pertaining to FHLB (Detail) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Federal Home Loan Banks [Abstract]    
Year of Maturity, 2018, Amount $ 150,000 $ 315,000
Total FHLB advances $ 150,000 $ 315,000
Year of Maturity, 2018, Weighted-Average Interest Rate 1.41%  
Year of Maturity, Total, Weighted-Average Interest Rate 1.41%