Common Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2017

Equity [Abstract]

Weighted Average Number of Common Shares Used In the Computation of Basic and Diluted Earnings per Share

The weighted average number of shares used in the computation of net income per share was as follows:

	2017	2016	2015
Basic	124,843,240	122,650,997	124,040,313
Diluted	129,017,613	128,552,838	130,188,866

Schedule of Changes in Shares of Common Stock Outstanding

Changes in shares of common stock outstanding, net of treasury shares, are presented below. Shares of common stock issued and outstanding do not include shares related to unissued restricted stock units (including shares held in the grantor trust).

	2017		2016		2015
Balance, beginning of year	121,193,599		123,307,837		126,748,836
Shares issued	1,052,256		281,654		1,061,026
Shares repurchased	(731,003	)	(2,395,892	)	(4,502,025)
Balance, end of year	121,514,852		121,193,599		123,307,837