Fair Value Measurement (Narrative) (Details) $ / shares in Units, $ in Thousands, shares in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) $ / shares	Jun. 30, 2017 USD ($)	Oct. 14, 2016 shares
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ 538	$ 8,703	$ 11,786	$ 19,555
Other Contract [Member] | Other Nonoperating Income (Expense) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ 602	9,946	$ 12,289	21,063
Measurement Input, Discount for Lack of Marketability [Member] | Level III [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Inputs, Discount for Lack of Marketability (Deprecated 2018-01-31)	0.32		0.32
RLJE [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment Warrants, Exercise Price | $ / shares			$ 3.00
RLJE [Member] | Other Contract [Member] | Other Nonoperating Income (Expense) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	$ 1,500	$ 8,200	$ 9,600	$ 17,200
RLJE [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants Received per RLJE Investment Agreement | shares					20