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Commitments and Contingent Liabilities - Summary of Rental Expense (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Operating Leases Rent Expense [Abstract]      
Rent expense on all property and equipment rented $ 1,597 $ 1,524 $ 1,360