Fair Value Measurements - Schedule of Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Assets:
Restricted cash and investments	$ 36,761	$ 15,064
Fair Value Recurring Basis
Assets:
Restricted cash and investments	59,003	39,956
Marketable securities	20,433	16,957
Liabilities:
Other liabilities related to restricted investments	7,903
Fair Value Recurring Basis | Level 1
Assets:
Restricted cash and investments	13,857	19,481
Marketable securities	12,665	9,515
Fair Value Recurring Basis | Level 2
Assets:
Restricted cash and investments	2,221	4,467
Marketable securities	7,768	7,442
Fair Value Recurring Basis | Level 3
Assets:
Restricted cash and investments	42,925	$ 16,008
Liabilities:
Other liabilities related to restricted investments	$ 7,903