Stockholders' Equity

12 Months Ended

Dec. 31, 2020

Stockholders' Equity Note [Abstract]

Shares of our common stock outstanding and activity for the years ended December 31, 2020, 2019 and 2018 are presented below:


	Years Ended December 31,
	2020	2019	2018

Common shares outstanding at January 1	161,846,525	172,121,491	177,407,622
Vesting of performance units	296,801	592,602	115,596
Vesting of restricted stock with performance feature	553,381	412,465	543,396
Forfeitures of restricted stock	—	(13,807)	(58,497)
Purchase of treasury stock (1)	(283,047)	(11,266,226)	(5,886,626)
Common shares outstanding at December 31	162,413,660	161,846,525	172,121,491

(1)Includes 283,047, 415,466 and 369,255 shares, respectively, withheld under the terms of stock-based compensation agreements to provide funds for the payment of payroll and income taxes due at the vesting of share-based awards, as well as other stock repurchases under separate authority from our Board of Directors.

In November 2019, our Board of Directors approved a $1.0 billion share repurchase program, which replaced all existing share repurchase programs authorizing us to repurchase common stock in the open market or through privately negotiated transactions. The timing and amount of stock repurchases will depend on market conditions and corporate, regulatory and other relevant considerations. This program may be discontinued at any time by the Board of Directors. As of December 31, 2020, we had not repurchased common stock under this stock repurchase program. In addition, we are authorized by our Board of Directors to repurchase shares in an amount sufficient to offset shares issued under our compensation programs.

During the years ended December 31, 2020, 2019 and 2018, we withheld shares of our common stock from certain employees in the amounts of $7.6 million, $21.9 million and $19.6 million, respectively. These withholdings were made under the terms of restricted stock unit and performance share unit agreements upon vesting, at which time, we concurrently made cash payments to fund payroll and income taxes on behalf of officers and employees who elected to have shares withheld from vested amounts to pay such taxes.