Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Consolidated Statements of Income [Abstract]
Revenue	$ 2,679,008	$ 2,279,099	$ 2,207,797
Cost of sales	634,140	502,078	500,457
Gross profit	2,044,868	1,777,021	1,707,340
Operating expenses:
Selling expenses	1,071,020	938,024	922,083
General and administrative expenses	662,302	564,514	554,153
Restructuring and impairment expenses	70,686	0	0
Total operating expenses	1,804,008	1,502,538	1,476,236
Operating income	240,860	274,483	231,104
Other income (expense), net (Note 20)	(21,194)	(8,916)	(18,265)
Income before provision for income taxes	219,666	265,567	212,839
Provision for income taxes	97,779	136,130	69,753
Net income	$ 121,887	$ 129,437	$ 143,086
Net income per share:
Basic (in dollars per share)	$ 2.21	$ 2.45	$ 2.58
Diluted (in dollars per share)	$ 2.16	$ 2.36	$ 2.55
Weighted-average common shares outstanding:
Basic (in shares)	55,170	52,806	55,412
Diluted (in shares)	56,476	54,852	56,097