12. Net Income (Loss) per Common Share

Basic net income (loss) per share excludes dilution for potentially dilutive securities and is computed by dividing net income (loss) by the weighted average number of common shares outstanding during the period. Diluted net income (loss) per share reflects the potential dilution under the treasury method that could occur if securities or other contracts to issue common stock were exercised or converted into common stock. For periods where the Company has presented a net loss, potentially dilutive securities are excluded from the computation of diluted net loss per share as they would be antidilutive. During 2015, 1,800,000 shares of the Company’s common stock, which were loaned to Bank of America pursuant to the terms of a share lending agreement, were issued and outstanding, with the holder of the borrowed shares having all the rights of a holder of the Company’s common stock. As the share borrower was required to return all borrowed shares to the Company, the borrowed shares were not considered outstanding for the purpose of computing and reporting basic or diluted loss per share during the period presented for 2015. These shares were returned to the Company in the third quarter of 2015.

The following tables summarize the components of the basic and diluted net income (loss) per common share computations (in thousands, except per share amounts):

	Year Ended December 31,
	2017			2016		2015
Basic EPS:
Net (loss) income (numerator)	$	(117,333	)	$	125,664	$	(368,445	)
Weighted average common shares (denominator)		104,245			92,053		81,233
Net (loss) income per share	$	(1.13	)	$	1.37	$	(4.54	)

Diluted EPS:
Net (loss) income (numerator)	$	(117,333	)	$	125,664	$	(368,445	)
Weighted average common shares		104,245			92,053		81,233

Effect of dilutive securities - common shares issuable		—			32		—
Adjusted weighted average common shares (denominator)		104,245			92,085		81,233

Net (loss) income per share	$	(1.13	)	$	1.36	$	(4.54	)

Common shares issuable represents incremental shares of common stock which consist of stock options, restricted stock units, warrants, and shares that could be issued upon conversion of the 2021 notes or the Facility Financing Obligation.

Potentially dilutive securities outstanding that are considered antidilutive are summarized as follows (in shares):

	December 31,
	2017		2016		2015
Exercise of common stock options		7,089,440		5,530,256		3,955,845
Conversion of convertible notes into common stock		6,875,272		814,561		814,561
Employee stock purchase plan		136,660		43,672		33,986
Exercise of common stock warrants		31,856		9,740,597		814,919
Vesting of restricted stock units		1,135,216		702,867		360,924
		15,268,444		16,831,953		5,980,235

Subsequent to December 31, 2017, the Company entered into an amendment to the Deerfield Facility Financing Obligation allowing additional principal amounts to be converted into equity. See Note 20 – Subsequent Events for further information.