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Debt (Senior Notes) (Details) - Senior notes - USD ($)
1 Months Ended
Sep. 30, 2012
Oct. 31, 2016
Jan. 31, 2016
Debt Instrument      
Debt, face value $ 350,000,000 $ 350,000,000 $ 350,000,000
Debt Instrument, Interest Rate, Stated Percentage 3.75%    
Proceeds from issuance of long-term debt $ 345,800,000    
Debt instrument, unamortized discount 1,300,000    
Payments of Debt Issuance Costs $ 2,900,000    
Debt redemption price as a percent of principal amount 100.00%    
Discount rate, basis spread on treasury rate 0.50%