Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Restricted Cash and Cash Equivalents Items [Line Items]
Cash	$ 56,086	$ 85,047
Cash equivalents	7,488	9,013
Restricted cash - letters of credit	4,400	4,300
Total cash and cash equivalents	68,022	98,313	$ 63,785	$ 69,962
Letter of Credit
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash - letters of credit	$ 4,448	$ 4,253