. 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 1, 2016.

Stock Option

Activity

The following table summarizes the

stock option activity for the

nine

months ended

September

30,

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		1,218		$	14.45
Exercised		(952	)	$	8.23
Expired and forfeited		(913	)	$	19.53
Balance at September 30, 2017		11,198		$	14.56		7.32

For the

nine

months ended

September 30, 2017,

952,000

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

$7.8

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

and

nine

months ended

September 30, 2017

and

2016

(in thousands):

	Three Months Ended September 30 ,				Nine Months Ended September 30,
	2017		2016		2017		2016

Research and development	$	2,595	$	3,946	$	8,758	$	8,347
General and administrative		2,419		1,763		7,345		5,229
Sales and marketing		2,462		1,802		7,544		5,121
Stock -based compensation expense included in operating expenses	$	7,476	$	7,511	$	23,647	$	18,697

Impact on basic and diluted net loss per share	$	0.14	$	0.19	$	0.45	$	0.50

As of

September 30, 2017,

there was $

62.1

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

2.5

years.

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:

	September 30 ,
	20 17			20 16
Risk-free interest rate		2.0	%		1.5	%
Dividend yield		0.0	%		0.0	%
Volatility		80.2	%		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

new offering periods for the

three

months ended

September 30, 2017

and

2016.