Quarterly Financial Data - Quarterly Results of Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Selected Quarterly Financial Information
Net Sales	$ 115,040	$ 115,651	$ 120,684	$ 117,625	$ 120,073	$ 118,859	$ 118,021	$ 113,530	$ 468,999	$ 470,483	$ 422,993
Gross margin	38,700	37,057	41,204	40,615	42,645	42,082	41,813	38,433	157,575	164,973	140,431
Operating earnings	12,391	(10,124)	(17,083)	(14,218)	(17,017)	(16,118)	(14,544)	(13,359)	(53,815)	(61,038)	(38,495)
Net earnings	$ 10,062	$ 2,722	$ 11,943	$ 11,419	$ 17,564	$ 10,211	$ 7,209	$ 11,548	$ 36,146	$ 46,532	$ 14,448
Basic net earnings per share (usd per share)	$ 0.31	$ 0.08	$ 0.36	$ 0.35	$ 0.53	$ 0.31	$ 0.22	$ 0.35	$ 1.11	$ 1.41	$ 0.44
Diluted net earnings per share (usd per share)	$ 0.31	$ 0.08	$ 0.36	$ 0.34	$ 0.52	$ 0.30	$ 0.21	$ 0.34	$ 1.09	$ 1.39	$ 0.43