12. Net income (loss) per share attributable to common stockholders

The following table sets forth the computation of basic and diluted net income (loss) per share attributable to common stockholders:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2013		2012		2013			2012
	(in thousands)
Numerator:
Net income (loss) attributable to common stockholders, basic and diluted	$	354	$	2,777	$	(1,166	)	$	5,895
Denominator:
Weighted average common stock, basic	35,593		35,080		35,620			34,618
Dilutive effect of stock options	1,347		2,257		—			2,706
Dilutive effect of RSUs	189		—		—			—
Weighted average common stock, dilutive	37,129		37,337		35,620			37,324
Net income (loss) per share attributable to common stockholders:
Basic	$	0.01	$	0.08	$	(0.03	)	$	0.17
Diluted	$	0.01	$	0.07	$	(0.03	)	$	0.16

For the three months ended September 30, 2013, 3,086,287 options to purchase common stock were not included in the computation of diluted net income per share as the inclusion would have been anti-dilutive. For the nine months ended September 30, 2013, we excluded all stock options and RSUs from the computation of diluted net loss per share due to the net loss for the period. For the three and nine months ended September 30, 2012, 2,478,156 and 2,442,898, respectively, options to purchase common stock were not included in the computation of diluted net income per share as the inclusion would have been anti-dilutive.