Quarterly Financial Data (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
Quarterly Financial Data (Unaudited) [Abstract]
Sales	$ 355,800	$ 340,300	$ 305,600	$ 279,500	$ 279,300	$ 231,700	$ 226,800	$ 194,400	$ 1,281,200	$ 932,135	$ 645,643
Gross profit	86,400	79,300	76,500	67,500	69,000	53,900	57,400	46,200	309,747	227,057	158,518
Net earnings	$ 25,400	$ 26,300	$ 19,300	$ 10,900	$ 20,700	$ 14,400	$ 18,500	$ 12,400	$ 81,857	$ 65,971	$ 43,823
Basic earnings per share (in dollars per share)	$ 0.78	$ 0.78	$ 0.57	$ 0.35	$ 0.68	$ 0.47	$ 0.61	$ 0.41	$ 2.48	$ 2.17	$ 1.46
Diluted earnings per share (in dollars per share)	$ 0.76	$ 0.78	$ 0.57	$ 0.34	$ 0.67	$ 0.47	$ 0.60	$ 0.40	$ 2.45	$ 2.14	$ 1.45