Debt Obligations - Interest Expense (Details) - 1.75% Convertible Senior Notes Due 2022 - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Nov. 30, 2017	Mar. 31, 2018
Line Of Credit Facility [Line Items]
Contractual interest expense		$ 875
Amortization of debt discount		2,197
Amortization of debt issuance costs	$ 4,600	229
Total interest expense related to the Notes		$ 3,301