Notes Payable - Additional Information (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	6 Months Ended			1 Months Ended	3 Months Ended	6 Months Ended		1 Months Ended	6 Months Ended	1 Months Ended	6 Months Ended		3 Months Ended
	Jul. 31, 2012	Jul. 31, 2011	Jul. 31, 2012 4.00% Debentures due 2031	Apr. 30, 2011 4.00% Debentures due 2031 Convertible Subordinated Debt	Jul. 31, 2012 4.00% Debentures due 2031 Convertible Subordinated Debt	Jul. 31, 2012 4.00% Debentures due 2031 Convertible Subordinated Debt	Jul. 31, 2012 6.25% Debentures due 2026, issued 2006	Mar. 31, 2006 6.25% Debentures due 2026, issued 2006 Convertible Subordinated Debt	Jul. 31, 2011 6.25% Debentures due 2026, issued 2006 Convertible Subordinated Debt	Apr. 30, 2010 Term Loan due 2013	Jul. 31, 2011 Term Loan due 2013	Jul. 31, 2010 Term Loan due 2013	Jul. 31, 2012 Other Notes Payable	Nov. 30, 2009 Other Notes Payable
Debt Instrument [Line Items]
Debt Instrument Amortization End Date					2018-03	2018-03
Issued Debt				$ 253,000						$ 20,000
Convertible debentures to common stock, conversion price					$ 20.538	$ 20.538
Convertible debentures to common stock, total number of share					12,319	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 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.		Accrued interest payments were payable quarterly in February, May, August, and November.
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.