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	$ 88,900	$ 79,941	$ 257,103	$ 250,137
Cost of goods sold	44,015	41,414	126,063	125,901
Gross profit	44,885	38,527	131,040	124,236
Operating expenses
Sales and marketing	10,478	10,075	33,248	31,892
General and administrative	13,609	12,076	37,727	35,549
Research and development	4,316	3,554	12,520	14,149
Total operating expenses	28,403	25,705	83,495	81,590
Operating income	16,482	12,822	47,545	42,646
Interest expense	4,446	4,442	12,794	14,147
Loss on extinguishment of debt	0	0	0	2,161
Other income	(799)	(908)	(2,055)	(2,037)
Income before income taxes	12,835	9,288	36,806	28,375
Income tax expense	3,566	762	9,581	2,116
Net income	$ 9,269	$ 8,526	$ 27,225	$ 26,259
Net income per common share:
Basic (in dollars per share)	$ 0.24	$ 0.23	$ 0.71	$ 0.71
Diluted (in dollars per share)	$ 0.24	$ 0.22	$ 0.69	$ 0.67
Weighted-average common shares outstanding:
Basic (in shares)	38,342	37,393	38,155	37,174
Diluted (in shares)	39,402	39,121	39,467	38,971