Fair Value Measurements, Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Cash Convertible Notes Hedges [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		$ 48,361
Purchases of Level 3 instruments		0
Settlements of Level 3 instruments		0
Gains (Losses) included in Earnings		85,718
Balance at end of period		134,079
Cash Conversion Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period		(48,361)
Purchases of Level 3 instruments		0
Settlements of Level 3 instruments		0
Gains (Losses) included in Earnings		(85,718)
Balance at end of period		(134,079)
Recurring [Member] | Cash Convertible Notes Hedges [Member]
Assets [Abstract]
Assets, gross fair value		134,079	$ 48,361
Assets, netting	[1]	0	0
Assets, net fair value		134,079	48,361
Recurring [Member] | Cash Convertible Notes Hedges [Member] | Level 3 [Member]
Assets [Abstract]
Assets, gross fair value		134,079	48,361
Recurring [Member] | Cash Conversion Derivative [Member]
Liabilities [Abstract]
Liabilities, gross fair value		134,079	48,361
Liabilities, netting	[1]	0	0
Liabilities, net fair value		134,079	48,361
Recurring [Member] | Cash Conversion Derivative [Member] | Level 3 [Member]
Liabilities [Abstract]
Liabilities, gross fair value		$ 134,079	$ 48,361

[1] This column reflects the impact of netting derivative assets and liabilities by counterparty when a legally enforceable master netting agreement exists.