Short-Term Borrowings - Additional Information (Detail) (Revolving credit facility, USD $) In Thousands, unless otherwise specified	6 Months Ended	9 Months Ended
	Oct. 31, 2013	Oct. 31, 2013
Line of Credit Facility [Line Items]
Termination date for senior, unsecured revolving credit facility	May 24, 2017
Revolving credit facility, maximum borrowing capacity	$ 125,000	$ 125,000
Credit facility limits, aggregate amount available for dividend and repurchase of stock		$ 50,000
Credit facility limits, aggregate amount available for dividend and repurchase of stock, percentage of cumulative net income		70.00%
Minimum
Line of Credit Facility [Line Items]
Commitment fee percentage on unused line of credit	0.30%
Minimum | LIBOR
Line of Credit Facility [Line Items]
Basis spread	2.00%
Minimum | Base rate
Line of Credit Facility [Line Items]
Basis spread	1.00%
Maximum
Line of Credit Facility [Line Items]
Commitment fee percentage on unused line of credit	0.40%
Maximum | LIBOR
Line of Credit Facility [Line Items]
Basis spread	2.50%
Maximum | Base rate
Line of Credit Facility [Line Items]
Basis spread	1.50%