Income Taxes - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jul. 31, 2013	Jul. 31, 2012	Jul. 31, 2013	Jul. 31, 2012
Income Tax Examination [Line Items]
Effective income tax rate	34.20%	34.60%	34.50%	34.50%
Unrecognized tax benefits, decreases resulting from current period tax positions	$ 20,000,000		$ 20,000,000
Minimum [Member]
Income Tax Examination [Line Items]
Income tax examination, tax years			2005
Minimum [Member] | Internal Revenue Service [Member]
Income Tax Examination [Line Items]
Income tax examination, tax years			2006
Minimum [Member] | New York state [Member]
Income Tax Examination [Line Items]
Income tax examination, tax years			2008
Minimum [Member] | New York City [Member]
Income Tax Examination [Line Items]
Income tax examination, tax years			2009
Maximum [Member] | Internal Revenue Service [Member]
Income Tax Examination [Line Items]
Income tax examination, tax years			2009
Maximum [Member] | New York state [Member]
Income Tax Examination [Line Items]
Income tax examination, tax years			2011
Maximum [Member] | New York City [Member]
Income Tax Examination [Line Items]
Income tax examination, tax years			2010