Summary of Significant Accounting Policies - Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Cash and cash equivalents	$ 50,436	$ 123,575	$ 77,627
Restricted cash	3,000	3,000	0
Total cash, cash equivalents and restricted cash shown in the statement of cash flow	$ 53,436	$ 126,575	$ 77,627	$ 120,210