Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2020

Stockholders' Equity Note [Abstract]

Schedules Shares of Common Stock Outstanding Activity

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.