Summary of Significant Accounting Policies - Restricted Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Restricted Assets
Restricted cash and cash equivalents	$ 49,227	$ 51,253	$ 56,211
Restricted short-term investments	88,867	82,772
Restricted deposits (included in other current assets)	43,547	36,215
Restricted long-term investments	1,026	2,307
Total	$ 182,667	$ 172,547
Equity in restricted net assets of consolidated subsidiaries as a percentage of consolidated stockholders' equity (as a percent)	9.30%