Consolidated Statements of Income (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Consolidated Statements of Income (Unaudited) [Abstract]
Revenue	$ 623,500	$ 704,190	$ 1,247,123	$ 1,320,409
Cost of sales	154,028	168,549	300,692	314,830
Gross profit	469,472	535,641	946,431	1,005,579
Operating expenses:
Selling expenses	245,828	272,757	495,536	530,459
General and administrative expenses	149,442	180,120	308,040	333,366
Total operating expenses	395,270	452,877	803,576	863,825
Operating income	74,202	82,764	142,855	141,754
Other income (expense), net	(3,326)	(11,165)	(6,174)	(9,958)
Income before provision for income taxes	70,876	71,599	136,681	131,796
Provision for income taxes	24,527	20,638	47,330	45,296
Net income	$ 46,349	$ 50,961	$ 89,351	$ 86,500
Net income per share (Note 2):
Basic (in dollars per share)	$ 0.83	$ 0.92	$ 1.61	$ 1.58
Diluted (in dollars per share)	$ 0.83	$ 0.90	$ 1.59	$ 1.53
Weighted-average common shares outstanding:
Basic (in shares)	55,536	55,608	55,486	54,807
Diluted (in shares)	55,943	56,713	56,030	56,430