Basis of Presentation (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Current Assets:
Cash and cash equivalents	$ 134,032	$ 60,115	$ 27,730
Restricted cash included in prepaid expenses and other current assets	228	2,000	2,000
Total cash, cash equivalents and restricted cash	$ 134,260	$ 62,115	$ 29,730	$ 54,592