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Debt (5.125% Senior Notes) (Details) - Senior Notes - 5.125% Senior Notes due 2023 - USD ($)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Mar. 19, 2013
Debt Instrument [Line Items]      
Stated interest rate 5.125% 5.125% 5.125%
Debt instrument, face amount     $ 300,000,000.0
Debt instrument, coupon rate 5.125%    
Debt instrument, yield to maturity 5.125%    
Debt instrument, payment terms Interest is payable semi-annually on April 1 and October 1 each year, beginning October 1, 2013.    
Debt instrument, frequency of payment semi-annually    
Debt instrument, commencement date of first required payment Oct. 01, 2013    
Debt instrument, maturity date Apr. 01, 2023    
Percentage of principal amount redeemable 101.00%    
Violation or event of default, interest payment failure, term 30 days    
Violation or event of default, interest payment failure, maximum excess proceeds on sale of asset $ 25,000,000.0    
Violation or event of default, interest payment failure, failure to comply with other indenture agreements, term 60 days    
Redemption, Period on or Prior To April 1, 2018      
Debt Instrument [Line Items]      
Redemption price calculation contributor, percentage 100.00%    
Minimum | Redemption, Period on or Prior To April 1, 2018      
Debt Instrument [Line Items]      
Notice period prior to redemption 30 days    
Minimum | Redemption, Period on or After April 1, 2018      
Debt Instrument [Line Items]      
Notice period prior to redemption 30 days    
Maximum | Redemption, Period on or Prior To April 1, 2018      
Debt Instrument [Line Items]      
Notice period prior to redemption 60 days    
Maximum | Redemption, Period on or After April 1, 2018      
Debt Instrument [Line Items]      
Notice period prior to redemption 60 days