Summary of Significant Accounting Policies - Reconciliation of Cash and Restricted Cash (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 88,668	$ 39,293
Restricted cash	7,033	12,772
Total cash, cash equivalents and restricted cash shown in the unaudited condensed consolidated statements of cash flows	95,701	52,065	$ 78,197	$ 122,255
Letter of Credit
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	7,033	7,628
Captive Insurance Subsidiary
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	0	$ 5,144
Initial Capitalization
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash	$ 1,500