Consolidated Statements of Income (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Consolidated Statements of Income (Unaudited) [Abstract]
Revenue	$ 589,934	$ 675,312	$ 1,837,057	$ 1,995,721
Cost of sales	140,162	157,457	440,854	472,287
Gross profit	449,772	517,855	1,396,203	1,523,434
Operating expenses:
Selling expenses	231,937	271,509	727,473	801,968
General and administrative expenses	147,943	165,671	455,983	499,037
Total operating expenses	379,880	437,180	1,183,456	1,301,005
Operating income	69,892	80,675	212,747	222,429
Other income (expense), net	(4,979)	(6,982)	(11,153)	(16,940)
Income before provision for income taxes	64,913	73,693	201,594	205,489
Provision for income taxes	20,823	20,547	68,153	65,843
Net income	$ 44,090	$ 53,146	$ 133,441	$ 139,646
Net income per share (Note 6):
Basic (in dollars per share)	$ 0.79	$ 0.96	$ 2.40	$ 2.54
Diluted (in dollars per share)	$ 0.79	$ 0.94	$ 2.39	$ 2.47
Weighted-average common shares outstanding:
Basic (in shares)	55,548	55,603	55,507	55,075
Diluted (in shares)	55,788	56,704	55,950	56,539