Quarterly Financial Data (Schedule of Quarterly Data) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended												12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2009	Sep. 30, 2009	Jun. 30, 2009	Mar. 31, 2009	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Net sales	$ 202,600	$ 206,700	$ 198,600	$ 206,800	$ 199,800	$ 192,200	$ 193,700	$ 180,100	$ 194,000	$ 186,700	$ 182,100	$ 174,900	$ 814,696	$ 765,769	$ 737,621
Gross profit	80,100	81,300	78,700	88,900	80,600	74,600	74,100	65,500	69,200	64,500	59,600	60,000	328,961	294,763	253,286
Net income/(loss)	$ (7,200)	$ 16,700	$ 8,800	$ 16,700	$ 20,500	$ 3,600	$ 7,900	$ 5,600	$ 3,700	$ (5,100)	$ (12,700)	$ (19,400)	$ 34,938	$ 37,636	$ (33,458)
Basic earnings per share	$ (0.23)	$ 0.53	$ 0.28	$ 0.54	$ 0.66	$ 0.12	$ 0.25	$ 0.18	$ 0.12	$ (0.17)	$ (0.41)	$ (0.64)	$ 1.12	$ 1.21	$ (1.09)
Diluted earnings per share	$ (0.23)	$ 0.53	$ 0.28	$ 0.53	$ 0.66	$ 0.12	$ 0.25	$ 0.18	$ 0.12	$ (0.17)	$ (0.41)	$ (0.64)	$ 1.11	$ 1.21	$ (1.09)
Cash dividends per share	$ 0.13	$ 0.13	$ 0.13	$ 0.12	$ 0.12	$ 0.12	$ 0.12	$ 0.12	$ 0.12	$ 0.12	$ 0.12	$ 0.12
Maximum [Member]
Class A Common Stock prices:	$ 25.7	$ 27.68	$ 27.9	$ 25.09	$ 25.62	$ 20.89	$ 25.73	$ 23.27	$ 22.87	$ 20.53	$ 14.69	$ 13.72
Minimum [Member]
Class A Common Stock prices:	$ 17.24	$ 17.82	$ 23.54	$ 21.84	$ 18.68	$ 15.06	$ 16.0	$ 18.32	$ 16.39	$ 10.05	$ 7.95	$ 5.05