Consolidated Statements of Income (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Consolidated Statements of Income (Unaudited) [Abstract]
Revenue	$ 623,623	$ 616,219
Cost of sales	146,664	146,281
Gross profit	476,959	469,938
Operating expenses:
Selling expenses	249,708	257,702
General and administrative expenses	158,598	153,246
Total operating expenses	408,306	410,948
Operating income	68,653	58,990
Other income (expense), net	(2,848)	1,207
Income before provision for income taxes	65,805	60,197
Provision for income taxes	22,803	24,658
Net income	$ 43,002	$ 35,539
Net income per share (Note 6):
Basic (in dollars per share)	$ 0.78	$ 0.66
Diluted (in dollars per share)	$ 0.77	$ 0.64
Weighted-average common shares outstanding:
Basic (in shares)	55,436	53,997
Diluted (in shares)	56,128	55,959