Quarterly Results (Unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2012
Quarterly Financial Information Disclosure [Abstract]
Net sales	$ 493,384	$ 482,372	$ 492,669	$ 462,792	$ 430,144	$ 416,047	$ 383,298	$ 352,134	$ 1,931,217	$ 1,581,623	$ 1,383,176
Gross profit	290,586	282,720	288,863	266,574	239,039	200,428	194,195	204,797	1,128,743	838,459	799,294
Operating income	126,037	116,918	117,508	98,401	56,713	17,413	8,094	96,333	458,864	178,553	396,516
Net income	$ 111,495	$ 105,401	$ 99,806	$ 78,579	$ 59,690	$ 10,173	$ (21,184)	$ 78,710	$ 395,281	$ 127,389	$ 336,705
Diluted net income per common share	$ 0.50	$ 0.48	$ 0.46	$ 0.37	$ 0.28	$ 0.05	$ (0.10)	$ 0.39	$ 1.82	$ 0.62	$ 1.65