Restricted Cash and Cash Equivalents - Reconciliation of Cash, Cash Equivalents and Restricted Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Cash And Cash Equivalents [Abstract]
Cash and cash equivalents	$ 53,676	$ 32,463	$ 54,030
Restricted cash and cash equivalents - current	27,229		33,536
Restricted cash and investments - non-current	40,970	30,923	33,728
Less Restricted investments - non-current	(32,787)		(26,341)
Total cash, cash equivalents and restricted cash and cash equivalents shown in the statement of cash flows	$ 89,088	$ 67,472	$ 94,953	$ 84,472