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, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	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, 2012	Dec. 31, 2011	Dec. 31, 2010
Net sales	$ 194,300	$ 194,600	$ 191,900	$ 180,100	$ 197,400	$ 200,300	$ 189,700	$ 200,000	$ 196,300	$ 186,600	$ 185,600	$ 174,500	$ 760,941	$ 787,287	$ 742,887
Gross profit	79,000	79,700	78,500	68,300	77,000	78,100	73,900	85,200	78,600	71,900	69,600	61,800	305,396	314,166	281,973
Net income	$ 8,200	$ 9,500	$ (33,700)	$ 47,000	$ (7,200)	$ 16,700	$ 8,800	$ 16,700	$ 20,500	$ 3,600	$ 7,900	$ 5,600	$ 30,977	$ 34,938	$ 37,636
Basic earnings per share	$ 0.27	$ 0.3	$ (1.08)	$ 1.5	$ (0.23)	$ 0.53	$ 0.28	$ 0.54	$ 0.66	$ 0.12	$ 0.25	$ 0.18	$ 0.99	$ 1.12	$ 1.21
Diluted earnings per share	$ 0.26	$ 0.3	$ (1.08)	$ 1.49	$ (0.23)	$ 0.53	$ 0.28	$ 0.53	$ 0.66	$ 0.12	$ 0.25	$ 0.18	$ 0.97	$ 1.11	$ 1.21
Cash dividends per share	$ 0.14	$ 0.14	$ 0.14	$ 0.13	$ 0.13	$ 0.13	$ 0.13	$ 0.12	$ 0.12	$ 0.12	$ 0.12	$ 0.12
Maximum [Member]
Class A Common Stock prices:	$ 22.68	$ 22.78	$ 24.7	$ 25.9	$ 25.7	$ 27.68	$ 27.9	$ 25.09	$ 25.62	$ 20.89	$ 25.73	$ 23.27
Minimum [Member]
Class A Common Stock prices:	$ 20.11	$ 17.66	$ 17.15	$ 22.35	$ 17.24	$ 17.82	$ 23.54	$ 21.84	$ 18.68	$ 15.06	$ 16.0	$ 18.32