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Long-Term Debt (Narrative 2016 Senior Notes) (Details) - Senior Notes - 2016 Senior Notes - USD ($)
Feb. 19, 2016
Mar. 31, 2021
Mar. 21, 2018
Debt Instrument [Line Items]      
Debt instrument, face amount $ 350,000,000.0   $ 250,000,000.0
Debt instrument, stated interest rate (as percent) 6.375% 6.375% 6.375%
Write off of deferred debt issuance cost $ 2,700,000    
Unamortized premium $ 9,600,000