Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Schedule of Company's liabilities that are measured at fair value on a recurring basis

The following tables present information about the Company’s liabilities that are measured at fair value on a recurring basis as of December 31, 2017 and 2016 and indicate the level of the fair value hierarchy utilized to determine such fair value (in thousands):

	Fair Value Measurements as of
	December 31, 2017 Using:
	Level 1		Level 2		Level 3		Total
Liabilities:
Liability for common stock warrants	$	—		—		194		194
Liability for deferred consideration		—		—		1,255		1,255
Liability for contingent consideration		—		—		12,319		12,319
	$	—		—		13,768		13,768

	Fair Value Measurements as of
	December 31, 2016 Using:
	Level 1		Level 2		Level 3		Total
Liabilities:
Liability for common stock warrants	$	—		—		99		99
Liability for deferred consideration		—		—		395		395
Liability for contingent consideration		—		—		1,242		1,242
	$	—		—		1,736		1,736

Schedule of aggregate fair values of the Company's common stock warrants and contingent consideration for which fair value is determined by Level 3 inputs

The following table provides a rollforward of the aggregate fair values of the Company’s common stock warrants, deferred and contingent consideration for which fair value is determined by Level 3 inputs (in thousands):  

Warrant Liability
Balance, December 31, 2016	$	99
Fair value of warrants to be issued upon borrowing under the SVB Loan Agreement (Note 5)		88
Warrants extinguished upon termination of SVB Loan Agreement		(88	)
Change in fair value through December 31, 2017		95
Balance, December 31, 2017	$	194
Deferred Consideration Liability
Balance, December 31, 2016	$	395
Initial fair value of acquisition-related deferred consideration		966
Change in fair value of deferred consideration		(106	)
Balance, December 31, 2017	$	1,255
Contingent Consideration Liability
Balance, December 31, 2016	$	1,242
Initial fair value of acquisition-related contingent consideration		9,946
Change in fair value of contingent consideration		1,131
Balance, December 31, 2017	$	12,319

Schedule of rollforward of the accrued warranties

The following table provides a rollforward of the accrued warranties (in thousands):

	Year Ended December 31,
	2017			2016
Beginning balance as of January 1	$	1,378		$	1,332
Assumed warranty liability from acquisition		137			—
Warranty costs incurred during the period		(167	)		(25	)
Changes in accrual related to warranties issued during the period		301			177
Changes in accrual related to pre-existing warranties		(7	)		(106	)
Balance as of December 31	$	1,642		$	1,378

Schedule of net loss per share, basic and diluted

	December 31,
	2017			2016			2015
Net loss (in thousands)	$	(64,028	)	$	(40,166	)	$	(41,230	)
Weighted average common shares outstanding, basic    and diluted		19,159,057			18,233,177			15,770,972
Net loss per share attributable to common stockholders	$	(3.34	)	$	(2.20	)	$	(2.61	)

Schedule of potentially dilutive securities excluded from the computation of diluted net loss per share attributable to common stockholders

The Company excluded the following potentially dilutive securities, outstanding as of December 31, 2017, 2016 and 2015 from the computation of diluted net loss per share attributable to common stockholders for the years ended December 31, 2017, 2016 and 2015 because they had an anti-dilutive impact due to the net loss attributable to common stockholders incurred for the periods.

	December 31,
	2017		2016		2015
Stock options to purchase common stock		1,867,627		2,057,296		1,967,906
Warrants for the purchase of common stock		47,710		47,710		47,710
		1,915,337		2,105,006		2,015,616

Stock Option

Schedule of fair value of employee stock options estimated using Black-Scholes option valuation model

The following table presents the weighted‑average assumptions used to estimate the fair value of options granted during the periods presented:

	Year Ended December 31,
Stock Options	2017						2016						2015
Expected term (in years)		4.47		to	6.07			5.47		to	6.07			5.27		to	6.08
Expected volatility		45	%	to	56	%		51	%	to	53	%		45	%	to	52	%
Risk-free interest rate		1.24	%	to	2.45	%		1.42	%	to	1.54	%		1.48	%	to	1.92	%
Dividend yield	—						—						—

Employee Stock Purchase Plan

Schedule of fair value of employee stock options estimated using Black-Scholes option valuation model

The following table presents the weighted-average assumptions used to estimate the fair value of the stock purchase rights granted under the employee stock purchase plan:

	Year Ended December 31,
ESPP	2017						2016						2015
Expected term (in years)		0.50		to	2.10			0.50		to	2.10			0.50		to	2.10
Expected volatility		46	%	to	55	%		42	%	to	58	%		42	%	to	44	%
Risk-free interest rate		0.08	%	to	1.30	%		0.08	%	to	0.85	%		0.08	%	to	0.71	%
Dividend yield	—						—						—