Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restricted Cash and Cash Equivalents Items [Line Items]
Cash	$ 59,455	$ 80,400
Cash equivalents	44,751	72,193
Restricted cash - letters of credit	9,800	3,800
Total cash and cash equivalents	113,975	156,374	$ 267,646	$ 98,313
Letter of Credit
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash - letters of credit	$ 9,769	$ 3,781