Cash and Marketable Securities - Schedule of Restricted Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	$ 137,184	$ 79,449	$ 62,936	$ 77,123
Restricted cash included within other non-current assets	1,500	1,500	1,500	1,500
Total cash, cash equivalents, and restricted cash	$ 138,684	$ 80,949	$ 64,436	$ 78,623