Condensed Consolidated Statements Of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement [Abstract]
Revenues	$ 328,004	$ 313,221	$ 611,152	$ 581,128
Cost of sales	146,604	143,414	289,879	277,737
Gross profit	181,400	169,807	321,273	303,391
Selling, general and administrative expenses	144,336	140,361	258,287	258,363
Income from operations	37,064	29,446	62,986	45,028
Foreign currency gains, net	283	162	1,354	438
Interest income	146	157	425	307
Interest expense	(132)	(188)	(245)	(372)
Other income, net	16	9	69	133
Income before income taxes	37,377	29,586	64,589	45,534
Income tax expense	3,000	7,627	13,758	12,564
Net income	34,377	21,959	50,831	32,970
Dividends on Series A convertible preferred stock	(3,000)	(3,000)	(6,000)	(6,000)
Dividend equivalents on Series A convertible preferred shares related to redemption value accretion and beneficial conversion feature	(951)	(873)	(1,882)	(1,729)
Net income attributable to common stockholders	$ 30,426	$ 18,086	$ 42,949	$ 25,241
Net income per common share:
Basic (in dollars per share)	$ 0.37	$ 0.21	$ 0.52	$ 0.29
Diluted (in dollars per share)	$ 0.35	$ 0.20	$ 0.51	$ 0.29
Weighted average common shares outstanding - basic (shares)	68,153	73,953	68,427	73,882
Weighted average common shares outstanding - diluted (shares)	71,467	74,572	70,462	74,625