Fair Value Measurements (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Sep. 25, 2017
Assets, Fair Value Disclosure [Abstract]
Convertible note hedge fair value	$ 56,046	$ 53,683
Liabilities, Fair Value Disclosure [Abstract]
Note conversion obligation fair value	56,881	54,359
Warrant liability	214,205	211,136
Fair Value, Measurements, Recurring [Member]
Assets, Fair Value Disclosure [Abstract]
Cash equivalents - money market	35,785	1,326
Derivative Asset	4,183	1,840
Convertible note hedge fair value	56,046	53,683
Total Assets	96,014	56,849
Liabilities, Fair Value Disclosure [Abstract]
Note conversion obligation fair value	(56,881)	(54,359)
Warrant liability	(214,205)	(211,136)
Total Liabilities	(271,086)	(265,495)
Carrying value, debt	530,400	515,800
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash equivalents - money market	0	0
Derivative Asset	0	0
Convertible note hedge fair value	0	0
Total Assets	0	0
Liabilities, Fair Value Disclosure [Abstract]
Note conversion obligation fair value	0	0
Warrant liability	0	0
Total Liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash equivalents - money market	35,785	1,326
Derivative Asset	4,183	1,840
Convertible note hedge fair value	56,046	53,683
Total Assets	96,014	56,849
Liabilities, Fair Value Disclosure [Abstract]
Note conversion obligation fair value	(56,881)	(54,359)	$ 57,369
Warrant liability	(214,205)	(211,136)
Total Liabilities	(271,086)	(265,495)
Difference between fair value and carrying value, debt	3,000	9,100
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Assets, Fair Value Disclosure [Abstract]
Cash equivalents - money market	0	0
Derivative Asset	0	0
Convertible note hedge fair value	0	0
Total Assets	0	0
Liabilities, Fair Value Disclosure [Abstract]
Note conversion obligation fair value	0	0
Warrant liability	0	0
Total Liabilities	$ 0	$ 0