Notes Payable - Additional Information (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended			1 Months Ended	3 Months Ended					1 Months Ended	3 Months Ended	1 Months Ended	3 Months Ended
	Apr. 30, 2012	Apr. 30, 2011	Apr. 30, 2012 4.00% Debentures due 2031	Apr. 30, 2011 4.00% Debentures due 2031 Convertible Subordinated Debt	Apr. 30, 2012 4.00% Debentures due 2031 Convertible Subordinated Debt	Apr. 30, 2012 4.00% Debentures due 2031 Convertible Subordinated Debt Redemption period April 1, 2018	Apr. 30, 2012 4.00% Debentures due 2031 Convertible Subordinated Debt Redemption period April 1, 2021	Apr. 30, 2012 4.00% Debentures due 2031 Convertible Subordinated Debt Redemption period April 1, 2026	Apr. 30, 2012 6.25% Debentures due 2026, issued 2006	Mar. 31, 2006 6.25% Debentures due 2026, issued 2006 Convertible Subordinated Debt	Apr. 30, 2011 6.25% Debentures due 2026, issued 2006 Convertible Subordinated Debt	Apr. 30, 2010 Term Loan due 2013	Apr. 30, 2011 Term Loan due 2013	Apr. 30, 2012 Other Notes Payable	Nov. 30, 2009 Other Notes Payable
Debt Instrument [Line Items]
Loan expiration period, in years												3 years
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.
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.
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 percentage	100.00%
Debt instrument amortization description					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
Redemption price						100.00%	100.00%	100.00%
Debt effective interest rate					7.25%
Redeemed amount of debt											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
Interest rate			4.00%						6.25%						3.875%
Other Notes Payable, due date														Nov. 17, 2012