Consolidated Statements of Income (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Consolidated Statements of Income (Unaudited) [Abstract]
Revenue	$ 563,698	$ 604,162	$ 1,612,898	$ 1,676,468
Cost of sales	120,832	125,863	353,619	391,937
Gross profit	442,866	478,299	1,259,279	1,284,531
Operating expenses:
Selling expenses	235,285	255,274	672,646	699,196
General and administrative expenses	143,219	140,651	411,270	415,014
Total operating expenses	378,504	395,925	1,083,916	1,114,210
Operating income	64,362	82,374	175,363	170,321
Other income (expense), net	(1,172)	(5,695)	(8,470)	(19,618)
Income before provision for income taxes	63,190	76,679	166,893	150,703
Provision for income taxes	21,518	19,807	55,691	45,802
Net income	$ 41,672	$ 56,872	$ 111,202	$ 104,901
Net income per share (Note 2):
Basic (in dollars per share)	$ 0.79	$ 1.02	$ 2.10	$ 1.87
Diluted (in dollars per share)	$ 0.76	$ 0.98	$ 2.04	$ 1.85
Weighted-average common shares outstanding:
Basic (in shares)	52,873	55,983	52,834	55,963
Diluted (in shares)	54,834	57,852	54,519	56,586