CONSOLIDATED STATEMENTS OF STOCKHOLDERS' INVESTMENT - USD ($) $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance		$ 1,257,847		$ 1,150,450	$ 1,257,847	$ 1,150,450	$ 1,047,015
Net income	$ 152,556	$ 122,080	$ 122,303	$ 118,963	504,893	513,384	509,699
Foreign currency translation adjustment					42,982	(23,496)	(9,336)
Dividends declared, $1.81 in 2017, $1.74 in 2016, and $1.57 in 2015 per share					(258,378)	(245,426)	(235,618)
Stock issued for employee benefit plans					$ 16,572	(17,405)	4,188
Issuance of restricted stock (in shares)					1,761,516
Issuance of restricted stock					$ 0	0	0
Stock-based compensation expense					41,814	38,554	58,067
Excess tax benefit on deferred compensation and employee stock plans						18,462	8,548
Repurchase of common stock					(179,985)	(176,676)	(232,113)
Ending Balance	$ 1,425,745		$ 1,257,847		$ 1,425,745	$ 1,257,847	$ 1,150,450
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance (in shares)		141,258,000		143,455,000	141,258,000	143,455,000	146,458,000
Beginning Balance		$ 14,126		$ 14,345	$ 14,126	$ 14,345	$ 14,646
Stock issued for employee benefit plans (in shares)					612,000	32,000	254,000
Stock issued for employee benefit plans					$ 61	$ 3	$ 25
Issuance of restricted stock (in shares)					97,000	221,000	164,000
Issuance of restricted stock					$ 10	$ 22	$ 16
Stock-based compensation expense (in shares)					1,000	17,000
Stock-based compensation expense						$ 3
Repurchase of common stock (in shares)					(2,426,000)	(2,467,000)	(3,421,000)
Repurchase of common stock					$ (243)	$ (247)	$ (342)
Ending Balance (in shares)	139,542,000		141,258,000		139,542,000	141,258,000	143,455,000
Ending Balance	$ 13,954		$ 14,126		$ 13,954	$ 14,126	$ 14,345
Additional Paid-in Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance		419,280		379,444	419,280	379,444	321,968
Stock issued for employee benefit plans					(16,760)	(16,121)	(9,095)
Issuance of restricted stock					(10)	(22)	(16)
Stock-based compensation expense					41,770	37,517	58,039
Excess tax benefit on deferred compensation and employee stock plans						18,462	8,548
Ending Balance	444,280		419,280		444,280	419,280	379,444
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance		3,190,578		2,922,620	3,190,578	2,922,620	2,648,539
Net income					504,893	513,384	509,699
Dividends declared, $1.81 in 2017, $1.74 in 2016, and $1.57 in 2015 per share					(258,378)	(245,426)	(235,618)
Ending Balance	3,437,093		3,190,578		3,437,093	3,190,578	2,922,620
Accumulated Other Comprehensive Loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance		(61,442)		(37,946)	(61,442)	(37,946)	(28,610)
Foreign currency translation adjustment					42,982	(23,496)	(9,336)
Ending Balance	(18,460)		(61,442)		(18,460)	(61,442)	(37,946)
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance		$ (2,304,695)		$ (2,128,013)	(2,304,695)	(2,128,013)	(1,909,528)
Stock issued for employee benefit plans					33,271	(1,287)	13,258
Stock-based compensation expense					44	1,034	28
Repurchase of common stock					(179,742)	(176,429)	(231,771)
Ending Balance	$ (2,451,122)		$ (2,304,695)		$ (2,451,122)	$ (2,304,695)	$ (2,128,013)