Consolidated Statements of Income (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Consolidated Statements of Income (Unaudited) [Abstract]
Revenue	$ 704,055	$ 612,366	$ 1,381,081	$ 1,130,394
Cost of sales	171,975	154,110	342,541	279,903
Gross profit	532,080	458,256	1,038,540	850,491
Operating expenses:
Selling expenses	277,893	248,628	551,639	454,670
General and administrative expenses	168,811	151,554	338,612	301,182
Total operating expenses	446,704	400,182	890,251	755,852
Operating income	85,376	58,074	148,289	94,639
Other income (expense), net	(4,012)	1,581	(2,430)	(4,593)
Income before provision for income taxes	81,364	59,655	145,859	90,046
Provision for income taxes	22,026	17,804	39,091	28,465
Net income	$ 59,338	$ 41,851	$ 106,768	$ 61,581
Net income per share (Note 6):
Basic (in dollars per share)	$ 1.18	$ 0.81	$ 2.12	$ 1.15
Diluted (in dollars per share)	$ 1.15	$ 0.81	$ 2.06	$ 1.15
Weighted-average common shares outstanding:
Basic (in shares)	50,115	51,872	50,409	53,466
Diluted (in shares)	51,557	51,925	51,850	53,502