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Debt and Financing Arrangements (Bank Debt) - Additional Information (Detail) - USD ($)
$ in Thousands
Sep. 30, 2018
Dec. 31, 2017
Debt Instrument [Line Items]    
Outstanding balance under applicable credit facility $ 167,100 $ 178,500
Outstanding letters of credit 900 2,300
2018 Credit Facility [Member]    
Debt Instrument [Line Items]    
Outstanding balance under applicable credit facility 167,100  
Available funds under credit facility 226,000  
Outstanding letters of credit $ 900  
2014 Credit Facility [Member]    
Debt Instrument [Line Items]    
Outstanding balance under applicable credit facility   $ 178,500