Notes Payable - Additional Information (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	9 Months Ended			9 Months Ended			9 Months Ended				3 Months Ended		9 Months Ended
	Oct. 31, 2012	Oct. 31, 2011	Oct. 31, 2012 4.00% Debentures due 2031	Oct. 31, 2012 4.00% Debentures due 2031 Convertible Subordinated Debt	Apr. 30, 2011 4.00% Debentures due 2031 Convertible Subordinated Debt	Oct. 31, 2012 6.25% Debentures due 2026, issued 2006	Oct. 31, 2011 6.25% Debentures due 2026, issued 2006 Convertible Subordinated Debt	Oct. 31, 2012 Term Loan due 2013	Oct. 31, 2011 Term Loan due 2013	Apr. 30, 2010 Term Loan due 2013	Oct. 31, 2012 Other Notes Payable	Nov. 30, 2009 Other Notes Payable	Oct. 31, 2012 Holder Optional Redemption Period 1 [Member] 4.00% Debentures due 2031 Convertible Subordinated Debt
Debt Instrument [Line Items]
Debt Instrument Amortization End Date				2018-03
Issued Debt					$ 253,000					$ 20,000
Convertible debentures to common stock, conversion price				$ 20.538
Convertible debentures to common stock, total number of share				12,319
Market price of common stock exceeding percent of the conversion price				120.00%
Market price of debentures declining to maximum percent of the value of the common stock				98.00%
Debentures Redemption Price	100.00%												100.00%
Debt effective interest rate				7.25%
Extinguishment of Debt, Amount							196,509		18,500
Loss on early extinguishment of debt before tax	0	3,518					11,192		312
Write-off of net unamortized debt discount							6,190
Premium on redemption							3,518
Write-off of unamortized debt issuance costs							$ 1,484
Term Loan Original Term								3 years
Debt Instrument, Frequency of Periodic Payment				Interest on the 4.00% Debentures is payable semi-annually in April and October.			Interest on the 6.25% Debentures was payable semi-annually in March and September.
Interest rate			4.00%			6.25%						3.875%
Other Notes Payable, due date											Nov. 17, 2012
Debt Instrument, Convertible, Terms of Conversion Feature				The market price of our common stock exceeding 120% of the conversion price; A call for redemption of the 4.00% Debentures; Specified distributions to holders of our common stock; If a fundamental change, such as a change of control, occurs; During the two months prior to, but not on, the maturity date; or The market price of the 4.00% Debentures declining to less than 98% of the value of the common stock into which the 4.00% Debentures are convertible.
Debt Instrument Amortization Description				The unamortized debt discount will be amortized to interest expense using the effective interest method through March 2018.