Summary of Significant Accounting Policies - Doubtful Accounts (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Changes in allowance for doubtful accounts
Beginning balance	$ 79,000	$ 89,000
Bad debt provision	67,000	(5,000)
Accounts written-off	(5,000)	(5,000)
Ending balance	$ 141,000	$ 79,000