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Employee Benefits - Summary of Nonvested Performance-Based Stock Units and Changes During Period (Detail) - Performance Based Restricted Stock Units [Member]
6 Months Ended
Jun. 30, 2017
$ / shares
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Granted | shares 72,274
Vested | shares 0
Cancelled | shares (471)
Nonvested performance-based stock awards, Ending balance | shares 71,803
Granted | $ / shares $ 52.00
Vested | $ / shares 0
Cancelled | $ / shares 52.00
Nonvested performance-based stock awards, Ending balance | $ / shares $ 52.00