Summary of Significant Accounting Policies (Details) - USD ($)	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2015
Accounting Policies [Abstract]
Balance of total restricted cash		$ 6,520,000
Cash and cash equivalents	$ 5,667,000	8,366,000	$ 10,203,000
Restricted cash included in current assets	1,520,000	1,020,000	6,020,000
Restricted cash included in long-term assets	5,000,000	5,000,000	0
Total cash, cash equivalents, and restricted cash shown in the Consolidated Statements of Cash Flows	$ 12,187,000	$ 14,386,000	$ 16,223,000	$ 17,846,000