Condensed Consolidated Statements Of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Revenues	$ 261,064	$ 243,273	$ 872,216	$ 824,401
Cost of sales	122,005	119,810	411,884	397,547
Gross profit	139,059	123,463	460,332	426,854
Selling, general and administrative expenses	125,164	120,778	383,451	379,141
Income from operations	13,895	2,685	76,881	47,713
Foreign currency gains (losses), net	233	(257)	1,587	181
Interest income	422	269	847	576
Interest expense	(126)	(167)	(371)	(539)
Other income, net	160	54	229	187
Income before income taxes	14,584	2,584	79,173	48,118
Income tax expense	4,092	955	17,850	13,519
Net income	10,492	1,629	61,323	34,599
Dividends on Series A convertible preferred stock	(3,000)	(3,000)	(9,000)	(9,000)
Dividend equivalents on Series A convertible preferred stock related to redemption value accretion and beneficial conversion feature	(972)	(892)	(2,854)	(2,621)
Net income (loss) attributable to common stockholders	$ 6,520	$ (2,263)	$ 49,469	$ 22,978
Net income (loss) per common share:
Basic (in dollars per share)	$ 0.08	$ (0.03)	$ 0.60	$ 0.26
Diluted (in dollars per share)	$ 0.07	$ (0.03)	$ 0.58	$ 0.26
Weighted average common shares outstanding - basic (shares)	67,821	71,895	68,223	73,212
Weighted average common shares outstanding - diluted (shares)	72,774	71,895	71,104	74,160