Fair Value Measurements (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fair Value Measurements
Amount outstanding under revolving credit agreement	$ 0	$ 3,240,000
Gains and losses on equity instruments
Net losses recognized during the period on equity investments	(90,000)
Less: net gains recognized during the period on equity investments sold during the period	(15,000)
Unrealized losses recognized during the period on equity investments still held at period end	(105,000)
Total
Fair Value Measurements
Equity investments	995,000	1,052,000
Total | Fair Value, Measurements, Nonrecurring
Fair Value Measurements
Long-lived assets held for sale	531,000	2,455,000
Level 1
Fair Value Measurements
Equity investments	995,000	1,052,000
Level 3 | Fair Value, Measurements, Nonrecurring
Fair Value Measurements
Long-lived assets held for sale	$ 531,000	$ 2,455,000