Summarized Quarterly Financial Data (unaudited) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Summarized Quarterly Financial Data Details
Revenue	$ 6,487,000	$ 7,884,000	$ 7,488,000	$ 8,177,000	$ 4,953,000	$ 3,089,000	$ 2,689,000	$ 2,379,000	$ 30,036,000	$ 13,110,000
Net income (loss)	$ 5,351,000	$ 3,119,000	$ 1,799,000	$ 1,693,000	$ 733,000	$ 1,001,000	$ 365,000	$ 58,000	$ 11,962,000	$ 2,157,000
Net income (loss) per share:
Continuing operations	$ 0.20	$ 0.11	$ 0.07	$ 0.06	$ 0.03	$ 0.05	$ 0.02	$ 0.00
Discontinued operations