Quarterly Financial Information (Unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Information (unaudited)
Net sales	$ 100,054	$ 78,836	$ 88,225	$ 36,396	$ 72,997	$ 52,026	$ 55,156	$ 14,141	$ 303,511	$ 194,320	$ 140,033
Gross profit	38,696	29,090	34,415	14,125	27,402	15,044	18,878	4,326	116,326	65,650	43,963
Income before taxes	20,682	16,555	22,417	2,343	14,605	694	9,261	(5,543)	61,997	19,017	10,156
Net income	$ 13,031	$ 10,762	$ 14,593	$ 1,575	$ 8,531	$ 603	$ 5,909	$ (3,404)	$ 39,352	$ 11,460	$ 5,943
Basic income per common share (in dollars per share)	$ 0.58	$ 0.48	$ 0.65	$ 0.07	$ 0.38	$ 0.03	$ 0.26	$ (0.15)	$ 1.78	$ 0.52	$ 0.27
Earnings per common share assuming dilution (in dollars per share)	$ 0.58	$ 0.47	$ 0.64	$ 0.07	$ 0.38	$ 0.02	$ 0.26	$ (0.15)	$ 1.77	$ 0.51	$ 0.26
Cash dividends paid per share (in dollars per share)	$ 0.22	$ 0.22	$ 0.22	$ 0.22	$ 0.21	$ 0.21	$ 0.21	$ 0.21