Restricted Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	$ 54,030	$ 31,255	$ 66,007
Restricted cash and cash equivalents - current	33,536		54,931
Restricted cash and investments - non-current	33,728		28,939
Less Restricted investments - non-current	(26,341)		(23,176)
Total cash, cash equivalents and restricted cash and cash equivalents shown in the statement of cash flows	$ 94,953	$ 84,472	$ 126,701	$ 133,545