Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Restricted Cash and Cash Equivalents Items [Line Items]
Balance of total restricted cash	$ 3,255
Cash and cash equivalents	11,664	$ 12,039	$ 3,912
Restricted cash included in current assets	2,768	6,020	6,520
Restricted cash included in long-term assets	487	0	0
Total cash, cash equivalents, and restricted cash shown in the Consolidated Statements of Cash Flows	14,919	$ 18,059	$ 10,432	$ 14,386
Restricted Until Maturity Date
Restricted Cash and Cash Equivalents Items [Line Items]
Balance of total restricted cash	3
Restricted Until Expiration of Agreement December 2020
Restricted Cash and Cash Equivalents Items [Line Items]
Balance of total restricted cash	$ 0