Fair-Value Measurements (Narrative) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized gain from valuation of derivatives	$ 31,118	$ (5,666)
Senior unsecured notes, net of debt issuance costs	2,463,171		$ 2,469,937
Fair value of senior unsecured notes	1,800,000		$ 2,500,000
Embedded Derivative Financial Instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized gain from valuation of derivatives	$ 32,500	$ 3,000
Equity Volatility
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Embedded derivative liability, measurement input	0.50