Annual report pursuant to Section 13 and 15(d)

Debt (Schedule of Debt Obligation) (Details)

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Debt (Schedule of Debt Obligation) (Details) - USD ($)
Dec. 31, 2021
Dec. 31, 2020
Aug. 31, 2020
May 31, 2018
Credit Agreement        
Outstanding debt obligations        
Revolving credit facility $ 0 $ 0    
Convertible Notes due 2023        
Outstanding debt obligations        
Face amount 345,000,000 345,000,000   $ 345,000,000
Unaccredited discount on convertible notes 0 (24,058,000)   $ (48,000,000)
Unamortized issuance costs on convertibe notes (2,979,000) (4,306,000)    
Convertible Notes 342,021,000 316,636,000    
Convertible Notes due 2025        
Outstanding debt obligations        
Face amount 517,500,000 517,500,000 $ 517,500,000  
Unaccredited discount on convertible notes 0 (65,902,000) $ (70,600,000)  
Unamortized issuance costs on convertibe notes (10,659,000) (11,731,000)    
Convertible Notes $ 506,841,000 $ 439,867,000