Organization and Basis of Presentation - Additional information (Details Textual) - USD ($)	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accumulated deficit	$ (444,329,000)	$ (416,383,000)
Cash, cash equivalents, and marketable securities	55,249,000
Working Capital	$ 37,323,000
Sufficient capital to fund its operations	1 year
Restricted cash	$ 758,000	$ 758,000
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets	736,000
Capitalized Contract Cost, Amortization	$ 258,000
Instruments
Product Warranty Liability
Product warranty period	one year
Reagents
Product Warranty Liability
Product warranty period	sixty day