Restricted Cash and Cash Equivalents - Reconciliation of Cash, Cash Equivalents and Restricted Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Cash And Cash Equivalents [Abstract]
Cash and cash equivalents	$ 75,734	$ 32,463	$ 21,561
Restricted cash and cash equivalents - current	28,345		56,343
Restricted cash and investments - non-current	32,703	30,923	27,358
Less Restricted investments - non-current	(30,081)		(25,708)
Total cash, cash equivalents and restricted cash and cash equivalents shown in the statement of cash flows	$ 106,701	$ 67,472	$ 79,554	$ 84,472