Quarterly Financial Data - Quarterly Results of Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Selected Quarterly Financial Information
Net sales	$ 110,910	$ 106,243	$ 105,686	$ 100,154	$ 101,584	$ 99,697	$ 98,693	$ 96,705	$ 422,993	$ 396,679	$ 382,310
Gross margin	32,875	37,538	35,794	34,224	35,861	36,641	34,457	33,468	140,431	140,428	127,109
Operating earnings (loss)	(19)	(13,111)	(13,208)	(12,196)	(14,146)	(12,490)	(24,097)	(12,433)	(38,495)	(63,166)	(18,113)
Net (loss) earnings	$ (13,621)	$ 9,619	$ 9,966	$ 8,484	$ 8,310	$ 3,720	$ 14,487	$ 7,863	$ 14,448	$ 34,380	$ 6,954
Basic earnings per share (usd per share)	$ (0.41)	$ 0.29	$ 0.30	$ 0.26	$ 0.25	$ 0.11	$ 0.44	$ 0.24	$ 0.44	$ 1.05	$ 0.21
Diluted earnings per share (usd per share)	$ (0.41)	$ 0.29	$ 0.30	$ 0.25	$ 0.25	$ 0.11	$ 0.44	$ 0.24	$ 0.43	$ 1.03	$ 0.21