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Debt Obligations and Credit Facilities - Senior Notes (Details) - Senior Notes - USD ($)
May 28, 2019
Mar. 10, 2017
Dec. 31, 2019
Dec. 31, 2018
Senior Notes        
Debt Instrument [Line Items]        
Aggregate principal amount   $ 350,000,000.0    
Interest rate   4.50% 4.50%  
Redemption price, percentage of principal amount   100.00%    
Debt issuance costs   $ 2,900,000    
Unamortized costs of debt     $ (1,400,000) $ (1,900,000)
Senior Notes Due 2029        
Debt Instrument [Line Items]        
Aggregate principal amount $ 500,000,000.0      
Interest rate 4.95%   4.95%  
Redemption price, percentage of principal amount 100.00%      
Debt issuance costs $ 6,800,000      
Unamortized costs of debt     $ (6,400,000)