Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2018

Stockholders' Equity Note [Abstract]

Changes To Equity

Shares of our common stock outstanding and activity for the years ended December 31, 2018, 2017 and 2016 are presented below:

	Years Ended December 31,
	2018		2017		2016
Common shares outstanding at January 1	177,407,622		177,345,266		180,234,388
Issuance of restricted stock, excluding restricted stock with performance feature	—		55,626		870,378
Vesting of performance units	115,596		138,374		76,404
Vesting of restricted stock with performance feature	543,396		350,063		40,294
Forfeitures of restricted stock	(58,497	)	(139,634	)	(16,795	)
Purchase of treasury stock (1)	(5,886,626	)	(342,073	)	(3,859,403	)
Common shares outstanding at December 31	172,121,491		177,407,622		177,345,266

(1) Includes 369,255, 342,073 and 147,922 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.