Consolidated Statements of Income (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Consolidated Statements of Income (Unaudited) [Abstract]
Revenue	$ 550,101	$ 600,475	$ 1,049,200	$ 1,072,306
Cost of sales	121,521	128,205	232,787	266,074
Gross profit	428,580	472,270	816,413	806,232
Operating expenses:
Selling expenses	228,353	248,363	437,361	443,922
General and administrative expenses	135,488	144,109	268,051	274,363
Total operating expenses	363,841	392,472	705,412	718,285
Operating income	64,739	79,798	111,001	87,947
Other income (expense), net	(2,731)	(11,060)	(7,298)	(13,923)
Income before provision for income taxes	62,008	68,738	103,703	74,024
Provision for income taxes	19,967	24,025	34,173	25,995
Net income	$ 42,041	$ 44,713	$ 69,530	$ 48,029
Net income per share (Note 2):
Basic (in dollars per share)	$ 0.79	$ 0.80	$ 1.32	$ 0.86
Diluted (in dollars per share)	$ 0.77	$ 0.79	$ 1.28	$ 0.85
Weighted-average common shares outstanding:
Basic (in shares)	52,929	55,952	52,804	55,953
Diluted (in shares)	54,839	56,356	54,466	56,388