Quarterly Financial Information - Unaudited (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Jan. 31, 2013	Oct. 31, 2012	Jul. 31, 2012	Apr. 30, 2012	Jan. 31, 2012	Oct. 31, 2011	Jul. 31, 2011	Apr. 30, 2011	Jan. 31, 2013	Jan. 31, 2012	Jan. 31, 2011
Notes To Financial Statements [Abstract]
Total revenues	$ 331,238	$ 268,760	$ 240,811	$ 247,918	$ 320,355	$ 250,508	$ 213,740	$ 230,035	$ 1,088,727	$ 1,014,638	$ 914,753
Gross profit	283,770	218,497	194,235	202,535	275,680	210,262	169,848	185,390	899,037	841,180	758,505
Operating Income	71,095	37,809	19,907	32,822	65,770	25,405	4,844	16,173	161,633	112,192	52,539
Net Income (Loss) Attributable to Parent	$ 61,746	$ 30,641	$ 18,167	$ 28,182	$ 57,820	$ 24,071	$ 4,334	$ (2,353)	$ 138,736	$ 83,872	$ 28,584
Basic (in dollars per share)	$ 0.50	$ 0.27	$ 0.17	$ 0.26	$ 0.53	$ 0.22	$ 0.04	$ (0.02)	$ 1.20	$ 0.76	$ 0.27
Diluted (in dollars per share)	$ 0.49	$ 0.27	$ 0.16	$ 0.25	$ 0.52	$ 0.22	$ 0.04	$ (0.02)	$ 1.17	$ 0.74	$ 0.26