Bank Revolving Credit Facility (Details Textual) (USD $)					12 Months Ended
	Jan. 31, 2013		Jan. 31, 2012		Jan. 31, 2013 Revolving Credit Facility [Member] option	Jan. 31, 2013 LIBOR [Member] Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Maximum borrowings	$ 450,000,000	[1]	$ 450,000,000	[1]	$ 450,000,000
Credit agreement maturity date					March 30, 2014 and provides for one, 12-month extension option
Number of credit facility extension options					1
Term of credit facility extension option (in months)					12 months
Interest rate of borrowings					LIBOR, subject to a floor of 100 basis points, plus 3.75%
Debt instrument variable rate basis					LIBOR
Debt instrument floor rate						1.00%
Debt instrument variable rate basis spread						3.75%
Amount of available borrowing that can be used for letters of credit or surety bonds					$ 100,000,000

[1] The maximum borrowings under the Credit Facility was increased to $465,000,000 on February 21, 2013, upon entering into the fourth amendment to the Credit Facility, as discussed below.