Quarterly report pursuant to Section 13 or 15(d)

Debt Obligations - Credit Facility Current Borrowings (Detail)

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Debt Obligations - Credit Facility Current Borrowings (Detail) - USD ($)
$ in Thousands
Jun. 30, 2018
Dec. 31, 2017
Line of Credit Facility [Line Items]    
Amount borrowed under the credit facility $ 840,198 $ 668,427
Credit facility available for revolving loans or issuing new letters of credit 529,900  
Letters Of Credit and Bank Guarantees    
Line of Credit Facility [Line Items]    
Letters of credit and bank guarantees 439,900  
Letters Of Credit and Bank Guarantees | U S Dollar    
Line of Credit Facility [Line Items]    
Letters of credit and bank guarantees 240,700  
Letters Of Credit and Bank Guarantees | Primarily Canadian and Australian Dollars    
Line of Credit Facility [Line Items]    
Letters of credit and bank guarantees 199,200  
Borrowings Under Credit Facility    
Line of Credit Facility [Line Items]    
Amount borrowed under the credit facility 840,200  
Borrowings Under Credit Facility | U S Dollar    
Line of Credit Facility [Line Items]    
Amount borrowed under the credit facility 770,600  
Borrowings Under Credit Facility | Australian Dollars    
Line of Credit Facility [Line Items]    
Amount borrowed under the credit facility $ 69,600