Property and Equipment - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended		6 Months Ended
	Nov. 30, 2010 acre	Jul. 31, 2012	Jul. 31, 2011	Jul. 31, 2012	Jul. 31, 2011	Jan. 31, 2012
Property, Plant and Equipment [Line Items]
Depreciation and amortization expense		$ 23.3	$ 16.7	$ 45.7	$ 31.5
Fixed assets acquired under capital lease agreements		119.3		119.3		105.1
Accumulated amortization relating to computers, equipment and software under capital leases		43.1		43.1		31.7
Acres of undeveloped real estate purchased	14
Perpetual parking rights	23.3
Pre-construction costs capitalized		5.7		5.7
Total carrying value of the land, building improvements and perpetual parking rights		$ 321.1		$ 321.1