Fair-Value Measurements (Narrative) (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized (losses) gains from valuation of embedded derivatives			$ (30,729)	$ 19,582
Carrying value of senior unsecured notes	$ 2,929,000		2,929,000		$ 2,750,016
Fair value of senior unsecured notes	2,900,000		2,900,000		$ 2,700,000
Embedded Derivative Financial Instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized (losses) gains from valuation of embedded derivatives	$ 1,700	$ 6,700	$ (31,000)	$ 17,400
Equity Volatility
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Embedded derivative liability, measurement input	0.50		0.50