Summary of Significant Accounting Policies - Prepaid expenses and other (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Prepaid expense and other current assets
Insurance	$ 692,000	$ 554,000
Property taxes	322,000	296,000
Other	172,000	205,000
Prepaid expenses and other	$ 1,186,000	$ 1,055,000