Income Taxes - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jul. 31, 2014	Jul. 31, 2013	Jul. 31, 2014	Jul. 31, 2013
Income Tax Examination [Line Items]
Effective Income Tax Rate, Percent	35.50%	34.20%	35.30%	34.50%
Tax Legislation Impact	0.6		1.3
Valuation Allowance Release Impact			0.6
Unrecognized Tax Benefit Decrease	$ 20,231,000
Penalties and Interest Decrease	$ 4,605,000
Minimum [Member]
Income Tax Examination [Line Items]
Open Tax Year			2006
Minimum [Member] | Internal Revenue Service [Member]
Income Tax Examination [Line Items]
Income tax examination, tax years			2010
Maximum [Member] | Internal Revenue Service [Member]
Income Tax Examination [Line Items]
Income tax examination, tax years			2011