(5) NET LOSS PER COMMON SHARE

Potentially issuable shares of common stock include shares issuable upon the exercise of outstanding employee stock option awards, common stock issuable under the Company’s Employee Stock Purchase Plan (ESPP), unvested restricted stock units (RSUs), common stock held by the NQDC and contingent issuances of common stock related to convertible debt.

The table below presents potential shares of common stock that were excluded from the computation of basic and diluted earnings per common share as they were anti-dilutive using the if-converted or treasury stock method (in thousands of common shares):

	Three and Six Months Ended June 30,
	2018		2017
Options to purchase common stock		7,829		8,440
Common stock issuable under the 2018 Notes		3,983		3,983
Common stock issuable under the 2020 Notes		3,983		3,983
Common stock issuable under the 2024 Notes		3,970		—
Unvested restricted stock units		3,544		3,041
Common stock potentially issuable for ESPP purchases		433		387
Common stock held by the NQDC		208		224
Total number of potentially issuable shares		23,950		20,058

In connection with the issuance of to the Company’s 0.75% senior subordinated convertible notes due in 2018 (the 2018 Notes) and the Company’s 1.50% senior subordinated convertible notes due in 2020 (the 2020 Notes), the Company entered into capped call transactions with respect to 50% of the principal amount of the 2018 Notes and 50% of the principal amount of the 2020 Notes with certain hedge counterparties with conversion price of $94.15 per share. Although the Company’s stock price on June 29, 2018 (the last trading day before June 30, 2018) exceeded the conversion price, the potential effect of the capped call transactions and potential shares issuable under the 2018 Notes and the 2020 Notes were excluded from the calculation of diluted loss per share in the three and six months ended June 30, 2018 as they were anti-dilutive using the if-converted method. The potential effect of the capped call transactions with respect to the 2018 Notes and the 2020 Notes was excluded from the diluted net loss per share in the three and six months ended June 30, 2017 as the Company’s closing stock price on June 30, 2017 did not exceed the conversion price.