Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Revenues	$ 343,374	$ 331,378	$ 301,853
Cost of goods sold	168,489	169,243	164,073
Gross profit	174,885	162,135	137,780
Operating expenses
Sales and marketing	43,159	42,315	36,542
General and administrative	50,167	49,842	38,832
Research and development	17,071	18,125	12,203
Total operating expenses	110,397	110,282	87,577
Gain on sales of assets	0	0	6,385
Operating income	64,488	51,853	56,588
Interest expense	17,405	18,410	26,618
Debt retirement costs	0	0	1,896
Loss on extinguishment of debt	0	2,442	0
Other income	(2,465)	(8,638)	(220)
Income before income taxes	49,548	39,639	28,294
Income tax expense (benefit)	9,030	(83,746)	1,532
Net income	$ 40,518	$ 123,385	$ 26,762
Net income per common share:
Basic (in dollars per share)	$ 1.06	$ 3.31	$ 0.84
Diluted (in dollars per share)	$ 1.03	$ 3.17	$ 0.82
Weighted-average common shares outstanding:
Basic (in shares)	38,233	37,276	32,044
Diluted (in shares)	39,501	38,892	32,656