Stockholders’ Equity

2017

Common Stock Offering

January

2017,

we sold

14.1

million shares of our common stock at a public offering price of

$12.20

per share. We received total net proceeds of

$163.7

million (net of

$8.8

million in issuance costs) from the sale of the common stock.

Private Placement

Warrants

June

2011,

we sold shares of common stock and warrants to purchase common stock in a private placement. A total of

4.0

million warrants to purchase common stock at an exercise price of

$3.60

per share were issued as part of this private placement. All warrants were exercised prior to their expiration date of

July

2016.

Stock Option

Activity

The following table summarizes the stock option activity for the

three

months ended

March

31,

2017:

						Weighted-
						Average
				Weighted-		Remaining
				Average		Contractual
	Shares			Exercise		Term
	(in thousands)			Price		(Years)
Balance at January 1, 2017		11,845		$	14.44		7.60
Granted		416		$	13.65
Exercised		(197	)	$	9.38
Expired and forfeited		(215	)	$	19.73
Balance at March 31, 2017		11,849		$	14.40		7.47

For the

three

months ended

March

31,

2017,

197,000

shares of common stock were issued pursuant to the exercise of stock options, resulting in proceeds to us of

$1.8

million.

Stock-Based Compensation

The following table summarizes stock-based compensation expense related to stock-based payment awards granted pursuant to all of our equity compensation arrangements for the

three

months ended

March

31,

2017

and

2016

(in thousands):

	Three Months Ended March 31,
	2017		2016

Research and development	$	3,208	$	2,073
General and administrative		2,374		1,667
Sales and marketing		2,439		1,615
Stock-based compensation expense included in operating expenses	$	8,021	$	5,355

Impact on basic and diluted net loss per share	$	0.16	$	0.15

As of

March

31,

2017,

there was $

79.4

million of total unrecognized compensation cost related to non-vested, stock-based payment awards granted under all of our equity compensation plans and all non-plan option grants. Total unrecognized compensation cost will be adjusted for future changes in estimated forfeitures. We expect to recognize this compensation cost over a weighted-average period of

2.9

years.

We estimated the fair value of each option grant on the grant date using the Black-Scholes option pricing model with the following weighted-average assumptions:

	Three Months Ended March 31,
	20 17			20 16
Risk-free interest rate		2.1	%		1.6	%
Dividend yield		0.0	%		0.0	%
Volatility		87.3	%		90.6	%
Expected life (years)		6			6

We estimate the fair value of each purchase right granted under our

1997

Employee Stock Purchase Plan at the beginning of each new offering period using the Black-Scholes option pricing model. There were no new offering periods for the

three

months ended

March

31,

2017

and

2016.