Selected Quarterly Financial Data (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
Quarterly Financial Information Disclosure [Abstract]
Sales	$ 275,707	$ 267,294	$ 263,759	$ 258,711	$ 245,836	$ 247,121	$ 247,347	$ 221,026	$ 1,065,471	$ 961,330	$ 828,341
Deferred Tax Benefit Expense Valuation Allowance Adj Capital Loss Carryforwards									0
Gross profit	47,826	40,478	44,652	46,732	38,998	43,992	44,149	32,959
Net income (loss)	$ 26,157	$ (34,201)	$ 14,722	$ 18,165	$ (17,929)	$ 8,274	$ 44,204	$ 3,703	$ 24,842	$ 38,251	$ 24,466
Basic:
Basic	$ 0.79	$ (1.03)	$ 0.45	$ 0.55	$ (0.54)	$ 0.25	$ 1.34	$ 0.11	$ 0.75	$ 1.16	$ 0.75
Diluted:
Net income (in usd per share)	$ 0.79	$ (1.03)	$ 0.44	$ 0.55	$ (0.54)	$ 0.25	$ 1.34	$ 0.11	$ 0.75	$ 1.16	$ 0.75
Shares used to compute earnings (loss) per share:
Shares used to compute earnings (loss) per share, Basic (in shares)	33,103,000	33,110,000	33,074,000	32,982,000	32,948,000	32,954,000	32,961,000	32,920,000	33,067,800	32,945,961	32,761,793
Shares used to compute earnings (loss) per share, Diluted (in shares)	33,112,000	33,110,000	33,108,000	32,988,000	32,949,000	32,954,000	33,051,000	32,957,000	33,092,474	32,951,288	32,775,072