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Investment Securities - Summary of Interest Income Earned on Investment Securities (Detail) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Net Investment Income [Line Items]    
Total interest income from available-for-sale securities $ 10,645 $ 11,868
Total interest income from held-to-maturity securities 4,525 4,765
Total investment income 15,170 16,633
Investment securities available-for-sale [Member]    
Net Investment Income [Line Items]    
Taxable 10,309 11,445
Tax-advantaged 336 423
Investment securities held-to-maturity [Member]    
Net Investment Income [Line Items]    
Taxable 2,910 2,878
Tax-advantaged $ 1,615 $ 1,887