Quarterly Financial Information (Unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Quarterly Financial Information (Unaudited)
Net sales	$ 28,200	$ 37,774	$ 65,499	$ 8,560	$ 60,256	$ 53,495	$ 71,557	$ 23,490	$ 140,033	$ 208,798	$ 176,795
Gross profit	7,517	11,566	23,060	1,820	19,914	16,494	26,338	9,071	43,963	71,817	60,301
Income (loss) before taxes	(419)	3,091	13,719	(6,235)	9,167	6,291	15,389	(475)	10,156	30,372	2,534
Net income (loss)	$ (1,038)	$ 2,346	$ 8,972	$ (4,268)	$ 6,150	$ 3,967	$ 9,723	$ (800)	$ 6,012	$ 19,040	$ 1,662	$ 9,843
Basic net earnings (loss) per common share attributable to common shareholders (in dollars per share)	$ (0.05)	$ 0.11	$ 0.41	$ (0.19)	$ 0.28	$ 0.18	$ 0.44	$ (0.04)	$ 0.27	$ 0.87	$ 0.09
Earnings (loss) per common share assuming dilution attributable to common shareholders (in dollars per share)	$ (0.05)	$ 0.10	$ 0.40	$ (0.19)	$ 0.28	$ 0.18	$ 0.44	$ (0.04)	$ 0.26	$ 0.85	$ 0.09
Cash dividends declared per share (in dollars per share)	$ 0.21	$ 0.21	$ 0.21	$ 0.21	$ 0.21	$ 0.20	$ 0.20	$ 0.57	$ 0.82	$ 1.18	$ 0.38
Cash dividends paid per share (in dollars per share)	$ 0.21	$ 0.21	$ 0.21	$ 0.21	$ 0.21	$ 0.20	$ 0.20	$ 0.57