Convertible Notes - Schedule of Interest Expense (Details) - Senior Notes Due 2019 [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Debt Instrument [Line Items]
Contractual interest expense	$ 1,797	$ 1,797	$ 5,391	$ 5,391
Amortization of debt issuance costs	1,045	1,021	3,117	3,045
Amortization of debt discount	8,536	8,284	25,418	24,667
Debt Instrument, Interest Expense, Total	$ 11,378	$ 11,102	$ 33,926	$ 33,103