Summary of Significant Accounting Policies - New Accounting Pronouncements (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Change in Contract with Customer, Liability [Abstract]
Beginning balance				$ 1,812	$ 1,057
Deferred revenues added				600	313
Elimination of deferred revenues due to joint venture liquidation				(986)	0
Previously deferred revenues recognized				(338)	(311)
Ending balance		$ 1,088	$ 1,059	1,088	1,059
Revenues	[1]	7,917	8,337	15,754	16,040
Net loss		$ (1,222)	$ (1,177)	$ (2,601)	$ (2,438)
Basic and diluted net loss per share (usd per share)		$ (0.27)	$ (0.26)	$ (0.57)	$ (0.55)
Accounts receivable, net		$ 3,147		$ 3,147		$ 2,296
Deferred cost of revenues		840		840		1,039
Deferred revenues		1,088		1,088		1,812
Total stockholders’ equity		$ 21,573		$ 21,573		23,727
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Change in Contract with Customer, Liability [Abstract]
Revenues			$ 8,021		$ 15,820
Net loss			$ (1,370)		$ (2,569)
Basic and diluted net loss per share (usd per share)			$ (0.31)		$ (0.58)
Accounts receivable, net						2,721
Deferred cost of revenues						1,767
Deferred revenues						4,805
Total stockholders’ equity						21,887
Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Change in Contract with Customer, Liability [Abstract]
Revenues			$ 316		$ 220
Net loss			$ 193		$ 131
Basic and diluted net loss per share (usd per share)			$ 0.05		$ 0.03
Accounts receivable, net						(425)
Deferred cost of revenues						(728)
Deferred revenues						(2,993)
Total stockholders’ equity						$ 1,840

[1] Represents the portfolio of available for sale securities that is included in restricted investments and short-term investments in the Company’s condensed consolidated balance sheets