Basis of Presentation and Summary of Significant Accounting Policies - Textual (Details)	3 Months Ended				12 Months Ended
	Mar. 31, 2018 USD ($) operating_segment	Mar. 31, 2018 USD ($)	Mar. 31, 2018 USD ($) segment	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($) segment	Dec. 31, 2016 USD ($)
Loss Contingencies [Line Items]
Cash and cash equivalents	$ 24,300,000	$ 24,300,000	$ 24,300,000	$ 13,923,000	$ 31,219,000
Cash	17,500,000	17,500,000	17,500,000		24,400,000
Money market funds	$ 6,800,000	6,800,000	$ 6,800,000		$ 6,800,000
Impairment charge		0				$ 0
Number of operating segments	2		2		1
Expense (benefit) from income taxes		(2,000)		24,000
Advertising expense		100,000		100,000
Provisional reduction to offsetting valuation allowance		34,100,000
Increase in accumulated deficit	$ 324,291,000	324,291,000	$ 324,291,000		$ 315,065,000
Revenues		14,042,000		7,971,000
Goodwill	3,241,000	3,241,000	3,241,000		3,241,000
Financial Standby Letter of Credit [Member]
Loss Contingencies [Line Items]
Restricted cash deposit balances	700,000	700,000	700,000	$ 700,000	700,000
India [Member]
Loss Contingencies [Line Items]
Non-current restricted cash	800,000	800,000	800,000		800,000
Accounting Standards Update 2016-01 [Member]
Loss Contingencies [Line Items]
Reclassified unrealized loss		500,000
Tax related to unrealized loss		600,000
Effect of change - higher (lower) [Member] | Accounting Standards Update 2014-09 [Member]
Loss Contingencies [Line Items]
Expense (benefit) from income taxes		0
Increase in accumulated deficit	$ 1,554,000	1,554,000	$ 1,554,000		$ 4,100,000
Revenues		$ 3,837,000