Bank Revolving Credit Facility (Details Textual) (USD $)			3 Months Ended
	Apr. 30, 2013	Jan. 31, 2013	Apr. 30, 2013 Revolving Credit Facility [Member]	Apr. 30, 2013 Common Class A or B [Member] Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Maximum borrowings	$ 465,000,000	$ 450,000,000	$ 465,000,000
Maximum borrowing capacity under accordion provision			500,000,000
Credit agreement maturity terms			February 21, 2016 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 plus 3.50%
Debt instrument variable rate basis			LIBOR
Debt instrument variable rate basis spread			3.50%
Amount of available borrowing that can be used for letters of credit or surety bonds			100,000,000
Maximum Class A common stock repurchase amount			100,000,000
Maximum dividend restriction in any four fiscal quarter period				$ 24,000,000