Consolidated Statements of Income (Unaudited) (USD $) In Thousands, except Share data in Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Consolidated Statements of Income (Unaudited) [Abstract]
Revenue	$ 682,927	$ 593,235	$ 1,233,021	$ 1,055,237
Cost of sales	111,273	95,584	201,318	171,340
Gross profit	571,654	497,651	1,031,703	883,897
Operating expenses:
Selling expenses	308,769	267,363	550,652	469,898
General and administrative expenses	148,302	132,376	283,809	244,424
Total operating expenses	457,071	399,739	834,461	714,322
Operating income	114,583	97,912	197,242	169,575
Other income (expense), net	(1,187)	(3,369)	(1,075)	266
Income before provision for income taxes	113,396	94,543	196,167	169,841
Provision for income taxes	38,961	34,136	67,450	61,605
Net income	$ 74,435	$ 60,407	$ 128,717	$ 108,236
Net income per share (Note 2):
Basic (in dollars per share)	$ 1.27	$ 0.98	$ 2.20	$ 1.75
Diluted (in dollars per share)	$ 1.22	$ 0.94	$ 2.11	$ 1.67
Weighted-average common shares outstanding (000s):
Basic (in shares)	58,620	61,706	58,487	62,016
Diluted (in shares)	61,121	64,230	60,882	64,773