CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Revenues	$ 312,766	$ 261,064	$ 967,614	$ 872,216
Cost of sales	148,942	122,005	476,796	411,884
Gross profit	163,824	139,059	490,818	460,332
Selling, general and administrative expenses	123,940	125,164	370,525	383,451
Income from operations	39,884	13,895	120,293	76,881
Foreign currency gains (losses), net	585	233	(893)	1,587
Interest income	167	422	493	847
Interest expense	(2,505)	(126)	(6,743)	(371)
Other income (expense), net	(34)	160	(48)	229
Income before income taxes	38,097	14,584	113,102	79,173
Income tax expense	2,421	4,092	13,518	17,850
Net income	35,676	10,492	99,584	61,323
Dividends on Series A convertible preferred stock	0	(3,000)	0	(9,000)
Dividend equivalents on Series A convertible preferred stock related to redemption value accretion and beneficial conversion feature	0	(972)	0	(2,854)
Net income attributable to common stockholders	$ 35,676	$ 6,520	$ 99,584	$ 49,469
Net income per common share:
Basic (in dollars per share)	$ 0.52	$ 0.08	$ 1.40	$ 0.60
Diluted (in dollars per share)	$ 0.51	$ 0.07	$ 1.38	$ 0.58
Weighted average common shares outstanding:
Basic (in shares)	69,097	67,821	71,003	68,223
Diluted (in shares)	70,176	72,774	72,342	71,104