Stockholders' Equity

1.625% Exchange

As described in Note 7, “Debt,” we issued 1.8 million shares of our common stock in connection with the 1.625% Exchange in March 2018.

1.125% Warrants

In connection with the Call Spread Overlay transaction described in Note 8, “Derivatives,” in 2013, we issued 13.5 million warrants with a strike price of $53.8475 per share. Under certain circumstances, beginning in April 2020, if the price of our common stock exceeds the strike price of the 1.125% Warrants, we will be obligated to issue shares of our common stock subject to a share delivery cap. The 1.125% Warrants could separately have a dilutive effect to the extent that the market value per share of our common stock exceeds the applicable strike price of the 1.125% Warrants. Refer to Note 3, “Net Income (Loss) per Share,” for dilution information for the periods presented. We will not receive any additional proceeds if the 1.125% Warrants are exercised.

As described in Note 8, “Derivatives,” in June 2018, we entered into privately negotiated termination agreements with each of the Counterparties to partially terminate the Call Spread Overlay, in notional amounts corresponding to the aggregate principal amount of the 1.125% Convertible Notes purchased. We paid $113 million to the Counterparties for the termination of 2.4 million of the 1.125% Warrants outstanding, which resulted in a reduction of additional paid-in capital for the same amount. Following this transaction, 11.1 million of the 1.125% Warrants remain outstanding.

Share-Based Compensation

In connection with our equity incentive plans and employee stock purchase plan, approximately 276,000 shares of common stock vested or were purchased, net of shares used to settle employees’ income tax obligations, during the six months ended June 30, 2018.

We record share-based compensation as “General and administrative expenses” in the accompanying consolidated statements of operations. As of June 30, 2018, there was $46 million of total unrecognized compensation expense related to unvested restricted stock awards (RSAs), performance stock awards (PSAs), and performance stock units (PSUs), which we expect to recognize over a remaining weighted-average period of 3.1 years, 0.7 years and 2.6 years, respectively. This unrecognized compensation cost assumes an estimated forfeiture rate of 10.8% for non-executive employees as of June 30, 2018.

Also as of June 30, 2018, there was $12 million of total unrecognized compensation expense related to unvested stock options, which we expect to recognize over a weighted-average period of 2.3 years. No stock options were granted or exercised in the six months ended June 30, 2018.

Activity for RSAs, PSAs and PSUs, for the six months ended June 30, 2018, is summarized below:



	Restricted Stock Awards		Performance Stock Awards		Performance Stock Units		Total		Weighted Average Grant Date Fair Value
Unvested balance, December 31, 2017	401,804		84,762		91,828		578,394		$	58.35
Granted	346,491		—		211,969		558,460		73.43
Vested	(183,595	)	(32,929	)	—		(216,524	)	57.04
Forfeited	(124,690	)	(48,701	)	(101,320	)	(274,711	)	63.38
Unvested balance, June 30, 2018	440,010		3,132		202,477		645,619		69.69

The aggregate fair values of RSAs, PSAs and PSUs granted and vested are presented in the following table:



	Six Months Ended June 30,
	2018		2017
	(In millions)
Granted:
Restricted stock awards	$	25	$	19
Performance stock units	16		16
	$	41	$	35
Vested:
Restricted stock awards	$	14	$	20
Performance stock awards	3		15
Performance stock units	—		9
	$	17	$	44