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Fair Value Measurement - Additional Information (Detail) - USD ($)
6 Months Ended 12 Months Ended
Jun. 30, 2017
Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Transfers between level 1 to level 2, Assets $ 0 $ 0
Transfers between level 2 to level 1, Assets 0 0
Transfers between level 1 to level 2, Liabilities 0 0
Transfers between level 2 to level 1, Liabilities 0 0
Transfer into level 3 0 0
Transfer out of level 3 0 0
Carrying value of loans fully charged-off 0  
Securities held to maturity 559,518,000 602,536,000
Level 3 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Securities held to maturity $ 0 $ 0