Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2017

Stockholders' Equity Note [Abstract]

Changes To Equity

Shares of our common stock outstanding and activity for the years ended December 31, 2017, 2016 and 2015 are presented below:

	Years Ended December 31,
	2017		2016		2015
Common shares outstanding at January 1	177,345,266		180,234,388		196,086,090
Issuance of restricted stock, excluding restricted stock with performance feature	55,626		870,378		447,534
Vesting of performance units	138,374		76,404		136,896
Vesting of restricted stock with performance feature	350,063		40,294		43,774
Forfeitures of restricted stock	(139,634	)	(16,795	)	(51,332	)
Purchase of treasury stock (1)	(342,073	)	(3,859,403	)	(16,428,574	)
Common shares outstanding at December 31	177,407,622		177,345,266		180,234,388

(1) Includes 342,073, 147,922 and 151,967 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.