Restructuring Costs - Changes in Restructuring Balance (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Restructuring Reserve [Roll Forward]
Beginning balance, accrued restructuring	$ 19,000	$ 0
Additional accruals	0	335,000
Cash payments	(19,000)	(282,000)
Non-cash settlements		(34,000)
Ending balance, accrued restructuring	0	19,000
Employee Severance and Benefits
Restructuring Reserve [Roll Forward]
Beginning balance, accrued restructuring	19,000	0
Additional accruals	0	301,000
Cash payments	(19,000)	(282,000)
Non-cash settlements		0
Ending balance, accrued restructuring	0	19,000
Asset Impairments
Restructuring Reserve [Roll Forward]
Beginning balance, accrued restructuring	0	0
Additional accruals	0	34,000
Cash payments	0	0
Non-cash settlements		(34,000)
Ending balance, accrued restructuring	$ 0	$ 0