Quarterly Result of Operations (Unaudited) (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
Quarterly Financial Information Disclosure [Abstract]
Sales	$ 106,423	$ 90,250	$ 82,682	$ 81,562	$ 91,698	$ 79,600	$ 78,538	$ 75,748	$ 360,917	$ 325,584	$ 317,548
Segment profit	62,094	52,034	46,760	43,749	48,677	42,678	43,934	42,671	204,637	177,960	167,236
Net income	$ (11,058)	$ 1,628	$ (3,625)	$ (1,461)	$ 3,545	$ 1,090	$ 3,392	$ 3,080	$ (14,516)	$ 11,107	$ 12,813
Net (loss) income per share:
Basic (loss) EPS (in dollars per share)	$ (0.66)	$ 0.10	$ (0.22)	$ (0.09)	$ 0.21	$ 0.07	$ 0.20	$ 0.19	$ (0.87)	$ 0.67	$ 0.74
Diluted EPS (in dollars per share)	$ (0.66)	$ 0.10	$ (0.22)	$ (0.09)	$ 0.21	$ 0.07	$ 0.20	$ 0.19	$ (0.87)	$ 0.67	$ 0.74