Notes Payable - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended								12 Months Ended
	Jan. 31, 2014	Jan. 31, 2014	Jan. 31, 2013	Jan. 31, 2012	Jan. 31, 2014 4.00% Debentures due 2031 Convertible Subordinated Debt	Jan. 31, 2013 4.00% Debentures due 2031 Convertible Subordinated Debt	Jan. 31, 2012 4.00% Debentures due 2031 Convertible Subordinated Debt	Apr. 30, 2011 4.00% Debentures due 2031 Convertible Subordinated Debt	Jan. 31, 2012 6.25% Debentures due 2026, issued 2006	Jan. 31, 2012 6.25% Debentures due 2026, issued 2006 Convertible Subordinated Debt	Jan. 31, 2012 Term Loan due 2013	Apr. 30, 2010 Term Loan due 2013
Debt Instrument
Repayments of principal in next five years	$ 0	$ 0
Issued debt								253,000,000				20,000,000
Interest rate								4.00%	6.25%
Conversion rate					49.133			48.6902
Principal amount multiple					1,000			1,000
Conversion price					$ 20.35			$ 20.54
Total number of shares					12,431,000
Market price of common stock exceeding percent of the conversion price					120.00%
Conversion circumstance stock price					$ 24.42
Threshold trading days					20
Threshold consecutive trading days					30 days
Market price of debentures declining to maximum percent of the value of the common stock					98.00%
If-converted value in excess of principal	5,565,000
Interest rate during period					7.25%	7.25%	7.25%
Extinguishment of debt, amount										196,509,000	18,500,000
Loss on early extinguishment of debt before tax										11,192,000	312,000
Write-off of net unamortized debt discount										6,190,000
Premium on redemption		0	0	3,518,000						3,518,000
Write-off of unamortized debt issuance costs										$ 1,484,000
Term loan original term											3 years