Quarterly Results (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Net sales									$ 433,947	$ 405,232	$ 383,977
Gross profit	$ 27,795	$ 32,763	$ 27,585	$ 15,390	$ 31,075	$ 35,658	$ 31,678	$ 24,986	103,533	123,397	118,080
Net income	$ 12,536	$ 14,085	$ 11,691	$ 4,260	$ 15,770	$ 14,717	$ 13,794	$ 10,217	$ 42,572	$ 54,498	$ 53,376
Earnings per share:
Basic (usd per share)	$ 0.24	$ 0.27	$ 0.22	$ 0.08	$ 0.30	$ 0.28	$ 0.26	$ 0.19	$ 0.81	$ 1.04	$ 1.01
Diluted (usd per share)	$ 0.24	$ 0.27	$ 0.22	$ 0.08	$ 0.30	$ 0.28	$ 0.26	$ 0.19	$ 0.81	$ 1.03	$ 1.00
Product
Disaggregation of Revenue [Line Items]
Net sales	$ 112,340	$ 112,937	$ 109,588	$ 99,082	$ 104,160	$ 113,668	$ 101,326	$ 86,078	$ 433,947	$ 405,232	$ 383,977