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Investment Securities (Disclosure Regarding Length of Time on Investment Securities with Temporary Impairment) (Detail) - USD ($)
$ in Thousands
Sep. 30, 2017
Dec. 31, 2016
Schedule of Held-to-maturity Securities [Line Items]    
Less than 12 months, fair value $ 73,380 $ 180,374
Less than 12 months, gross unrealized losses (1,027) (5,267)
12 months or longer, fair value 22,251 6,617
12 months or longer, gross unrealized losses (823) (304)
Total, fair value 95,631 186,991
Total, gross unrealized losses (1,850) (5,571)
Agency Obligations [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Less than 12 months, fair value 3,853 3,525
Less than 12 months, gross unrealized losses (55) (83)
12 months or longer, fair value 0 0
12 months or longer, gross unrealized losses 0 0
Total, fair value 3,853 3,525
Total, gross unrealized losses (55) (83)
State And Municipal Obligations [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Less than 12 months, fair value 62,881 172,152
Less than 12 months, gross unrealized losses (938) (5,132)
12 months or longer, fair value 22,251 6,617
12 months or longer, gross unrealized losses (823) (304)
Total, fair value 85,132 178,769
Total, gross unrealized losses (1,761) (5,436)
Corporate Obligations [Member]    
Schedule of Held-to-maturity Securities [Line Items]    
Less than 12 months, fair value 6,646 4,697
Less than 12 months, gross unrealized losses (34) (52)
12 months or longer, fair value 0 0
12 months or longer, gross unrealized losses 0 0
Total, fair value 6,646 4,697
Total, gross unrealized losses $ (34) $ (52)