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Debt Obligations - Credit Facility Current Borrowings (Detail) - USD ($)
$ in Thousands
Jun. 30, 2017
Dec. 31, 2016
Line of Credit Facility [Line Items]    
Amount borrowed under the credit facility $ 480,690 $ 351,341
Credit facility available for revolving loans or issuing new letters of credit 1,000,000  
Letters Of Credit and Bank Guarantees    
Line of Credit Facility [Line Items]    
Letters of credit and bank guarantees under the credit facility 324,700  
Letters Of Credit and Bank Guarantees | U S Dollar    
Line of Credit Facility [Line Items]    
Letters of credit and bank guarantees under the credit facility 225,100  
Letters Of Credit and Bank Guarantees | Primarily Canadian and Australian Dollars    
Line of Credit Facility [Line Items]    
Letters of credit and bank guarantees under the credit facility 99,600  
Borrowings Under Credit Facility    
Line of Credit Facility [Line Items]    
Amount borrowed under the credit facility 480,700  
Borrowings Under Credit Facility | U S Dollar    
Line of Credit Facility [Line Items]    
Amount borrowed under the credit facility 326,400  
Borrowings Under Credit Facility | Canadian Dollars    
Line of Credit Facility [Line Items]    
Amount borrowed under the credit facility $ 154,300