Fair Value Measurements - Schedule of Assets Measured at Fair Value on a Recurring Basis (Details) - Fair Value Recurring Basis - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Assets:
Restricted cash and investments	$ 27,162	$ 42,609
Marketable securities	31,385	34,634
Level 1
Assets:
Restricted cash and investments	11,036	11,276
Marketable securities	24,301	27,103
Level 2
Assets:
Restricted cash and investments	2,115	2,050
Marketable securities	7,084	7,531
Level 3
Assets:
Restricted cash and investments	$ 14,011	$ 29,283