Convertible Notes - Schedule of Interest Expense (Details) - Senior Notes Due 2019 [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Debt Instrument [Line Items]
Contractual interest expense	$ 1,797	$ 1,797	$ 3,594	$ 3,594
Amortization of debt issuance costs	1,039	1,015	2,071	2,024
Amortization of debt discount	8,472	8,222	16,882	16,383
Debt Instrument, Interest Expense, Total	$ 11,308	$ 11,034	$ 22,547	$ 22,001