Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Restricted Cash and Cash Equivalents Items [Line Items]
Cash	$ 45,234	$ 85,047
Cash equivalents	2,503	9,013
Restricted cash - letters of credit	4,300	4,300
Total cash and cash equivalents	51,993	98,313	$ 55,600	$ 69,962
Letter of Credit
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash - letters of credit	$ 4,256	$ 4,253