Leases - Maturities of lease liabilities - Long-term lease obligations (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Leases
Total lease payments	$ 3,437,000	$ 5,239,000
Less: imputed interest	(744,000)	(816,000)
Total lease obligations	2,693,000	4,423,000
Less: current obligations	(1,023,000)	(1,304,000)
Long-term lease obligations	$ 1,670,000	$ 3,119,000