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Fair Value Measurements - Narrative (Details) - Senior Notes [Member] - USD ($)
Dec. 31, 2019
Oct. 31, 2019
Sep. 30, 2019
Dec. 31, 2018
Apr. 15, 2015
$400 Million 5% Senior Notes [Member]          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Face amount $ 400,000,000       $ 400,000,000
Stated interest rate (as a percent) 5.00%       5.00%
Debt amount $ 396,778,000     $ 395,903,000  
Fair value of notes 409,000,000.0        
$700 Million 4.75% Senior Note [Member]          
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Face amount $ 700,000,000 $ 700,000,000 $ 700,000,000    
Stated interest rate (as a percent) 4.75% 4.75% 4.75%    
Debt amount $ 690,626,000        
Fair value of notes $ 724,100,000