Derivative Instruments and Hedging Activities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Derivatives in Cash Flow Hedging Relationships [Abstract]
Loss related to effective portion of derivatives recognized in accumulated OCI, gross of tax effect	$ 0	$ 110
Loss related to effective portion of derivatives reclassified from accumulated OCI to interest expense, gross of tax effect	0	(507)
Liabilities [Abstract]
Derivative liabilities, current	134,079	0
Derivative liabilities, long-term	0	$ 48,361
Cash Flow Hedging [Member]
Derivatives, Fair Value [Line Items]
Fixed interest rate		1.48%
Cash Convertible Notes Hedges [Member] | Selling, General and Administrative Expenses [Member]
Net unrealized gain (loss) on derivative instruments not designated as hedging instruments [Abstract]
Net unrealized gain (loss)	85,718	$ 35,729
Cash Convertible Notes Hedges [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Assets [Abstract]
Derivative assets, current	134,079	0
Derivative assets, long-term	0	48,361
Cash Conversion Derivative [Member] | Selling, General and Administrative Expenses [Member]
Net unrealized gain (loss) on derivative instruments not designated as hedging instruments [Abstract]
Net unrealized gain (loss)	(85,718)	(35,729)
Cash Conversion Derivative [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Liabilities [Abstract]
Derivative liabilities, current	134,079	0
Derivative liabilities, long-term	$ 0	$ 48,361