Method of Overhead Allocation (Detail) (USD $) In Thousands, 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
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	$ 375,278	$ 543,513	$ 251,479	$ 229,449	$ 294,346	$ 510,009	$ 229,975	$ 196,871	$ 1,399,719	$ 1,231,201	$ 1,063,404
Long-Lived Assets	201,188				81,325				201,188	81,325	77,616
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									1,333,885	1,185,800	1,025,763
Long-Lived Assets	81,606				80,817				81,606	80,817	77,042
Non-United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									65,834	45,401	37,641
Long-Lived Assets	$ 119,582				$ 508				$ 119,582	$ 508	$ 574