Notes Payable - Additional Information (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	9 Months Ended	1 Months Ended		9 Months Ended				1 Months Ended	9 Months Ended			1 Months Ended	9 Months Ended	1 Months Ended
	Oct. 31, 2011	Oct. 31, 2011 4.00% Debentures due 2031 Convertible Subordinated Debt	Apr. 30, 2011 4.00% Debentures due 2031 Convertible Subordinated Debt	Oct. 31, 2011 4.00% Debentures due 2031 Convertible Subordinated Debt	Oct. 31, 2011 4.00% Debentures due 2031 Convertible Subordinated Debt Redemption period April 1, 2018	Oct. 31, 2011 4.00% Debentures due 2031 Convertible Subordinated Debt Redemption period April 1, 2021	Oct. 31, 2011 4.00% Debentures due 2031 Convertible Subordinated Debt Redemption period April 1, 2026	Mar. 31, 2006 6.25% Debentures due 2026, issued 2006 Convertible Subordinated Debt	Oct. 31, 2011 6.25% Debentures due 2026, issued 2006 Convertible Subordinated Debt	Oct. 31, 2010 6.25% Debentures due 2026, issued 2006 Convertible Subordinated Debt	Oct. 31, 2011 6.25% Debentures due 2026, issued fiscal 2011	Apr. 30, 2010 Term Loan due 2013	Oct. 31, 2011 Term Loan due 2013	Nov. 30, 2009 Other Notes Payable
Debt Instrument [Line Items]
Loan expiration period, in years												3 years
Issued Debt			$ 253,000					$ 200,000			$ 31,509	$ 20,000
Term Loan, fixed principal amount												500
Description of interest payment period			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.				Accrued interest payments were payable quarterly in February, May, August, and November.
Convertible debentures to common stock, conversion price		$ 20.538		$ 20.538
Convertible debentures to common stock, total number of share		12,319
Circumstances for the redemption of Debentures				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.
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%
Description of amortization of debt discount				The unamortized debt discount will be amortized to interest expense using the effective interest method through March 2018.
Debt discount amortization period end		2018-03		2018-03
Redemption price					100.00%	100.00%	100.00%
Debt effective interest rate				7.25%					8.60%	8.60%
Redeemed amount of debt									196,509				18,500
Loss on early extinguishment of debt before tax	(3,518)								11,192				312
Write-off of net unamortized debt discount									6,190
Debt effective interest rate													4.81%
Premium on redemption									3,518
Write-off of unamortized debt issuance costs									$ 1,484
Interest rate														3.875%
Other Notes Payable, due date														Nov. 17, 2012