Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Balance of total restricted cash		$ 6,520
Cash and cash equivalents	$ 3,912	8,366	$ 6,576
Restricted cash included in current assets	6,520	1,020	1,020
Restricted cash included in long-term assets	0	5,000	5,000
Total cash, cash equivalents, and restricted cash shown in the Consolidated Statements of Cash Flows	$ 10,432	$ 14,386	$ 12,596	$ 17,846