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	$ 53,447	$ 59,455
Cash equivalents	21,492	44,751
Restricted cash - letters of credit	9,611	9,769
Total cash and cash equivalents	$ 84,550	$ 113,975	$ 109,720	$ 156,374