Bank Revolving Credit Facility (Details Textual) (USD $)		6 Months Ended		6 Months Ended
	Jan. 31, 2013	Jul. 31, 2013 Revolving credit facility [Member]	Jan. 31, 2013 Revolving credit facility [Member]	Jul. 31, 2013 Common stock Class A or B [Member] Revolving credit facility [Member]	Jul. 31, 2013 Senior Notes due 2017 [Member]	Jan. 31, 2013 Senior Notes due 2017 [Member]	Jul. 31, 2013 Senior Notes due 2034 [Member]	Jan. 31, 2013 Senior Notes due 2034 [Member]	Jul. 31, 2012 Senior Notes due 2034 [Member]
Line of Credit Facility [Line Items]
Total available borrowings	$ 450,000,000	$ 500,000,000	$ 465,000,000
Total available borrowing capacity under accordion provision		500,000,000
Credit Facility 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%
Variable rate basis of debt instrument		LIBOR
Variable rate basis spread of debt instrument		3.50%
Amount of available borrowings 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
Interest rate					6.50%	6.50%	7.375%	7.375%	7.375%