Investments and Fair Value Measurements (Additional Information Regarding Fair Value Measurements) (Details) - USD ($)	Jun. 30, 2021	Feb. 18, 2021	Dec. 31, 2020	Feb. 25, 2020	Nov. 15, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Carrying Value	$ 3,473,929,000		$ 1,732,622,000
Level 2 [Member] | Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Closing trading price per $100 as of the last day of trading for the quarter	100
Unsecured Debt [Member] | 2030 Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument, face amount	750,000,000.0			$ 750,000,000.0
Long-term Debt, Carrying Value	739,696,000
Unsecured Debt [Member] | 2030 Notes [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	789,338,000
Unsecured Debt [Member] | 2027 Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument, face amount	750,000,000.0				$ 750,000,000.0
Long-term Debt, Carrying Value	744,261,000
Unsecured Debt [Member] | 2027 Notes [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	851,858,000
Unsecured Debt [Member] | 2026 Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt instrument, face amount	750,000,000.0	$ 750,000,000.0
Long-term Debt, Carrying Value	742,021,000
Unsecured Debt [Member] | 2026 Notes [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	$ 741,173,000