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Long-Term Debt and Short-Term Borrowings - Revolving Credit Facility - Additional Information (Detail) - USD ($)
Jun. 30, 2017
Dec. 31, 2016
Debt Instrument [Line Items]    
Letters of credit outstanding amount $ 64,200,000  
Revolving credit facility [Member]    
Debt Instrument [Line Items]    
Revolving credit facility principal amount outstanding 0 $ 0
Letters of credit outstanding amount $ 2,000,000 $ 2,000,000