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Employee Benefit Plans - Additional Information (Detail)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2017
USD ($)
Sep. 30, 2017
USD ($)
Retirement Benefits [Abstract]    
Employer discretionary contribution amount $ 10,000  
Net periodic pension cost decline in expense 252 $ 748
Unrecognized actuarial gains (losses), before tax 53,991 53,991
Unrecognized actuarial gains (losses), net of tax 34,014 34,014
Amortization expected to be recognized $ 4,411 4,411
Amortization expected to be recognized, net of tax   $ 2,779