Significant Accounting Policies - Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Restricted cash
Cash and cash equivalents	$ 442,845	$ 419,693	$ 352,387
Restricted cash included in other current assets	850	300	5
Restricted cash included in other assets	500		500
Total cash, cash equivalents, and restricted cash shown in the statement of cash flows	$ 444,195	$ 420,497	$ 352,892	$ 312,237