CONSOLIDATED CONDENSED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Income Statement [Abstract]
Net sales	$ 230,504	$ 231,893	$ 514,683	$ 583,767
Cost of sales	128,807	141,087	285,720	328,064
Gross profit	101,697	90,806	228,963	255,703
Operating expenses:
Selling expense	59,966	60,604	126,285	137,915
General and administrative expense	15,536	12,545	31,635	30,541
Research and development expense	7,603	6,846	15,519	14,759
Total operating expenses	83,105	79,995	173,439	183,215
Income from operations	18,592	10,811	55,524	72,488
Interest income	276	282	347	325
Interest expense	(2,212)	(2,894)	(4,304)	(5,585)
Other income (expense), net	(2,021)	(2,957)	525	(5,200)
Income before income taxes	14,635	5,242	52,092	62,028
Income tax provision	1,817	1,873	3,455	3,347
Net income	$ 12,818	$ 3,369	$ 48,637	$ 58,681
Earnings per common share:
Basic (in dollars per share)	$ 0.16	$ 0.04	$ 0.62	$ 0.76
Diluted (in dollars per share)	$ 0.15	$ 0.04	$ 0.54	$ 0.66
Weighted-average common shares outstanding:
Basic (in shares)	78,395	77,633	78,076	77,502
Diluted (in shares)	94,913	78,560	94,406	93,367
Dividends paid per common share (usd per share)	$ 0.01	$ 0.01	$ 0.02	$ 0.02