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Debt - Additional Information (Details)
1 Months Ended 3 Months Ended 12 Months Ended
Aug. 31, 2015
USD ($)
Mar. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Debt Instrument [Line Items]      
Borrowings under the credit facility   $ 688,000,000 $ 576,500,000
4.7% senior notes due 2025      
Debt Instrument [Line Items]      
Face value $ 300,000,000    
Debt instrument, interest rate 4.70% 4.70%  
Debt instrument, maturity year 2025 2025  
Increase in senior notes interest rate 0.25%    
Effective interest rate   4.80%  
4.7% senior notes due 2025 | Level 2      
Debt Instrument [Line Items]      
Fair value of senior notes   $ 299,000,000  
Senior unsecured credit facility - revolving loan due 2019      
Debt Instrument [Line Items]      
Face value   700,000,000  
Repayments of debt $ 296,400,000    
Borrowings under the credit facility   391,000,000  
Maximum amount available under credit facility to issue letters of credit   40,000,000  
Letters of credit outstanding under credit facility   2,100,000  
Undrawn availability under credit facility   $ 306,900,000  
Debt instrument, covenant terms   In accordance with the terms of the Facility, we are required to maintain a minimum interest coverage ratio of 3.50 (based on the ratio of EBITDA, as defined in the credit agreement, to interest expense) and may not exceed a maximum leverage ratio of 3.50 (based on the ratio of total debt to EBITDA) throughout the term of the Facility.  
Average interest rate   1.90% 1.80%
Maximum | 4.7% senior notes due 2025      
Debt Instrument [Line Items]      
Debt instrument, interest rate 6.70%    
Maximum | Senior unsecured credit facility - revolving loan due 2019      
Debt Instrument [Line Items]      
Interest coverage ratio required to be maintained   3.50