Fair Value Measurements - Schedule of Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Assets:
Marketable securities	$ 36,071	$ 34,634
Fair Value Recurring Basis
Assets:
Restricted cash and investments	32,765	42,609
Marketable securities	36,071	34,634
Liabilities:
Other liabilities related to restricted investments	3,009
Fair Value Recurring Basis | Level 1
Assets:
Restricted cash and investments	8,018	11,276
Marketable securities	27,978	27,103
Liabilities:
Other liabilities related to restricted investments	0
Fair Value Recurring Basis | Level 2
Assets:
Restricted cash and investments	2,108	2,050
Marketable securities	8,093	7,531
Liabilities:
Other liabilities related to restricted investments	0
Fair Value Recurring Basis | Level 3
Assets:
Restricted cash and investments	22,639	29,283
Marketable securities	0	$ 0
Liabilities:
Other liabilities related to restricted investments	$ 3,009