Consolidated Statements of Income (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Consolidated Statements of Income (Unaudited) [Abstract]
Revenue	$ 641,152	$ 703,347	$ 2,022,233	$ 1,833,741
Cost of sales	158,907	183,374	501,448	463,277
Gross profit	482,245	519,973	1,520,785	1,370,464
Operating expenses:
Selling expenses	255,719	280,695	807,358	735,365
General and administrative expenses	161,142	165,050	499,754	466,232
Total operating expenses	416,861	445,745	1,307,112	1,201,597
Operating income	65,384	74,228	213,673	168,867
Other income (expense), net	2,781	525	351	(4,068)
Income before provision for income taxes	68,165	74,753	214,024	164,799
Provision for income taxes	18,436	18,446	57,527	46,911
Net income	$ 49,729	$ 56,307	$ 156,497	$ 117,888
Net income per share (Note 6):
Basic (in dollars per share)	$ 0.99	$ 1.10	$ 3.11	$ 2.24
Diluted (in dollars per share)	$ 0.97	$ 1.08	$ 3.03	$ 2.23
Weighted-average common shares outstanding:
Basic (in shares)	50,098	51,308	50,304	52,741
Diluted (in shares)	51,260	52,243	51,629	52,906