Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2017

Stockholders' Equity Note [Abstract]

Stock Option Plan Activity and Stock Options Granted

A summary of activities under our stock option plan consisted of the following:



	Options Outstanding		Exercise Price⁽¹⁾		Remaining Life⁽²⁾
Outstanding as of January 1, 2017	3,757,947		$	46.81	5.85
Granted	764,789		$	47.00	9.00
Exercised	(329,612	)	$	28.59
Cancelled/forfeited	(244,216	)	$	48.22
Outstanding as of December 31, 2017	3,948,908		$	48.28	5.89
Exercisable as of December 31, 2017	1,280,499		$	50.07	3.78



	Options Outstanding		Exercise Price⁽¹⁾		Remaining Life⁽²⁾
Outstanding as of January 1, 2016	4,530,982		$	41.49	4.89
Granted	845,440		$	46.00	8.41
Exercised	(1,180,242	)	$	24.80
Cancelled/forfeited	(438,233	)	$	49.49
Outstanding as of December 31, 2016	3,757,947		$	46.81	5.85
Exercisable as of December 31, 2016	1,200,250		$	45.93	3.74

⁽¹⁾Weighted average exercise price.

⁽²⁾Weighted average remaining contractual life in years.

The following tables summarize the details of options granted under our stock option plan that were still outstanding as of December 31, 2017, and the assumptions used to value those grants. All such grants were effective at the close of business on the date of grant.



	Options Granted	Option Exercise (Strike) Price		Closing Stock Price on Date of Grant		December 31, 2017
Date of Grant	Options Granted	Option Exercise (Strike) Price		Closing Stock Price on Date of Grant		Options Outstanding	Options Exercisable
January 3, 2017	764,789	$	47.00	$	46.95	713,097	—
April 19, 2016	845,440	$	46.00	$	45.74	738,611	—
April 21, 2015	893,220	$	42.00	$	41.26	674,499	142,072
April 22, 2014	955,000	$	56.00	$	50.53	567,500	158,750
April 16, 2013	205,000	$	54.00	$	49.25	101,750	55,250
April 17, 2012	1,235,000	$	54.00	$	49.01	952,001	772,977
April 19, 2011	410,000	$	35.00	$	31.78	60,350	35,350
April 20, 2010	530,000	$	30.00	$	27.13	79,550	54,550
April 21, 2009	790,000	$	27.00	$	17.61	61,550	61,550
Total	6,628,449					3,948,908	1,280,499

Fair Value Assumptions for Options Granted



Date of Grant	Risk-free Interest Rate		Expected Life of Option in Years	Expected Dividend Yield		Expected Stock Volatility		Estimated Fair Value of Stock Option
January 3, 2017	1.9	%	5.00	2.6	%	24.49	%	$	8.40
April 19, 2016	1.3	%	5.00	2.6	%	26.34	%	$	8.18
April 21, 2015	1.3	%	5.00	2.7	%	26.84	%	$	7.35
April 22, 2014	1.8	%	5.00	2.0	%	28.55	%	$	9.57
April 16, 2013	0.7	%	5.00	1.6	%	37.42	%	$	12.66
April 17, 2012	0.9	%	5.00	1.4	%	39.25	%	$	13.69
April 19, 2011	2.1	%	5.00	1.6	%	39.33	%	$	11.20
April 20, 2010	2.6	%	5.00	1.5	%	39.10	%	$	8.14
April 21, 2009	1.9	%	5.00	1.0	%	38.80	%	$	3.64

Reconciliation of Denominators used in Computation of Basic and Diluted Earnings per Share

The following tables present a reconciliation of the denominators used in the computation of basic and diluted earnings per share and a summary of the options to purchase shares of common stock which were excluded from the diluted earnings calculation because they were anti-dilutive:



Reconciliation	2017	2016	2015
Basic weighted average shares outstanding	288,208,435	288,949,525	291,453,107
Weighted shares assumed upon exercise of stock options	134,298	207,998	592,335
Diluted weighted average shares outstanding	288,342,733	289,157,523	292,045,442

Anti-Dilutive Options Excluded



Summary of Anti-dilutive Options Excluded	2017		2016	2015
Options to purchase shares of common stock	3,524,401		3,095,343	2,611,367
Weighted average exercise prices of options	$	49.85	50.09	51.89