Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)		3 Months Ended
	Jan. 01, 2019	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Summary Of Significant Accounting Policies [Line Items]
Accumulated deficit		$ (228,572,000)		$ (221,043,000)
Impact to revenue		$ 12,728,000	$ 10,152,000
Revenue, performance obligation, description of warranty		The Company provides a two-year warranty on all new System sales which were determined to be assurance-type warranties and thus not considered a separate performance obligation. The Company accrues the cost of providing these warranties
Right of return or refund		$ 0
Term of distribution agreement		7 years 6 months
Distribution agreement, renewal period		2 years
Revenue recognized		$ 1,100,000
ASU 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606
Summary Of Significant Accounting Policies [Line Items]
Accumulated deficit	$ 0	0
Impact to revenue	$ 0	$ 0
Topic 842
Summary Of Significant Accounting Policies [Line Items]
Accumulated deficit				$ 0