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Long-Term Debt and Short-Term Borrowings - Revolving Credit Facility - Additional Information (Detail) - USD ($)
Jun. 30, 2016
Dec. 31, 2015
Debt Instrument [Line Items]    
Outstanding borrowings $ 156,000,000  
Letters of credit outstanding amount 48,000,000  
Revolving credit facility [Member]    
Debt Instrument [Line Items]    
Outstanding borrowings 156,000,000 $ 0
Letters of credit outstanding amount $ 2,000,000 $ 2,000,000
2015 Credit Agreement [Member]    
Debt Instrument [Line Items]    
Revolving credit facility, weighted average annual interest rates 2.20%