Net Income (Loss) Per Common Share

Basic net income (loss) per share attributable to common stockholders is calculated by dividing the net income (loss) attributable to common stockholders by the weighted-average number of common shares outstanding for the period, without consideration for common stock equivalents. Diluted net income (loss) per share is computed using the weighted average number of common shares outstanding and, when dilutive, potential common share equivalents from outstanding options and unvested RSUs settleable in shares of common stock (using the treasury-stock method), and potential common shares from convertible securities (using the if-converted method).

The following table sets forth the computation of basic and diluted net income (loss) per share (in millions, except per share data):



	Three Months Ended September 30,					Nine Months Ended September 30,
	2018		2017			2018		2017
Net income (loss)	$	46.6	$	(2.0	)	$	52.6	$	(40.8	)
Net income (loss) per common share:
Basic	$	0.53	$	(0.02	)	$	0.60	$	(0.47	)
Diluted	$	0.52	$	(0.02	)	$	0.59	$	(0.47	)

Basic weighted average shares outstanding	88.5		86.7			88.0		86.1
Effect of potentially dilutive stock options	0.2		—			0.2		—
Effect of potentially dilutive share-based awards	1.6		—			1.1		—
Diluted weighted average shares outstanding	90.3		86.7			89.3		86.1

Outstanding anti-dilutive securities not included in diluted net income (loss) per share attributable to common stockholders calculation (in millions):



	Three Months Ended September 30,		Nine Months Ended September 30,
	2018	2017	2018	2017
Options outstanding to purchase common stock	—	0.4	—	0.4
Unvested restricted stock units	—	2.8	0.3	2.8
Senior convertible notes	4.0	4.0	4.0	4.0
Total	4.0	7.2	4.3	7.2