Significant Accounting Policies - Cash and Cash Equivalents, and Long Term Restricted Cash (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Cash and cash equivalents	$ 48,707,000	$ 56,689,000	$ 48,315,000
Long term restricted cash included in other assets	0	547,000	488,000
Cash, cash equivalents and long term restricted cash shown in the consolidated statement of cash flows	$ 48,707,000	$ 57,236,000	$ 48,803,000	$ 49,708,000