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Long-Term Debt - Revolving Credit Facility - Additional Information (Detail) - Revolving credit facility
Jun. 30, 2017
USD ($)
Line of Credit Facility [Line Items]  
Amount outstanding at the credit facility $ 0
Letter of credit sublimit as part of revolving credit facility 125,000,000
Amount withdrawn from revolving credit facility 1,600,000
Remaining borrowing capacity $ 498,400,000