Significant Accounting Policies - Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Significant Accounting Policies [Line Items]
Cash and cash equivalents	$ 167,422	$ 104,162	$ 81,699
Total cash, cash equivalents, and restricted cash	177,833	114,678	94,679	$ 127,946
Other Assets
Significant Accounting Policies [Line Items]
Restricted cash	10,018	10,325	9,967
Prepaid Expenses and Other Current Assets
Significant Accounting Policies [Line Items]
Restricted cash	$ 393	$ 191	$ 3,013