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Fair Value Measurements - Face Value, Carrying Amount and Fair Value of Financial Instruments (Details) - Senior unsecured notes - USD ($)
Jun. 30, 2021
Jun. 17, 2021
Dec. 31, 2020
May 10, 2017
2028 Senior unsecured notes payable        
Financial liabilities:        
Senior unsecured notes payable - face value $ 400,000,000 $ 400,000,000.0 $ 0  
2025 Senior unsecured notes payable        
Financial liabilities:        
Senior unsecured notes payable - face value 300,000,000.0   300,000,000 $ 300,000,000.0
Carrying Amount | Level 2 | 2028 Senior unsecured notes payable        
Financial liabilities:        
Senior unsecured notes payable 393,842,000   0  
Carrying Amount | Level 2 | 2025 Senior unsecured notes payable        
Financial liabilities:        
Senior unsecured notes payable 297,048,000   296,669,000  
Fair Value | Level 2 | 2028 Senior unsecured notes payable        
Financial liabilities:        
Senior unsecured notes payable 410,000,000   0  
Fair Value | Level 2 | 2025 Senior unsecured notes payable        
Financial liabilities:        
Senior unsecured notes payable $ 307,875,000   $ 311,430,000