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Debt - $350 Million 5% Senior Notes (Details) - Senior Notes [Member] - $350 Million 5% Senior Notes [Member] - USD ($)
12 Months Ended
Dec. 31, 2018
Apr. 03, 2013
Debt Instrument [Line Items]    
Face amount $ 350,000,000 $ 350,000,000
Stated interest rate (as a percent) 5.00% 5.00%
Debt instrument, maturity date Apr. 15, 2021  
Debt instrument, frequency of periodic payment semi-annually  
Redemption Period One [Member]    
Debt Instrument [Line Items]    
Redemption price (as a percent) 101.25%  
Redemption date Apr. 15, 2018  
Redemption Period Two [Member]    
Debt Instrument [Line Items]    
Redemption price (as a percent) 100.00%  
Redemption date Apr. 15, 2019