Notes Payable - Additional Information (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended			1 Months Ended		12 Months Ended						1 Months Ended	12 Months Ended					1 Months Ended	12 Months Ended		1 Months Ended
	Jan. 31, 2012	Jan. 31, 2010	Jan. 31, 2012 4.00% Debentures due 2031	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 4.00% Debentures due 2031 Convertible Subordinated Debt	Jan. 31, 2012 4.00% Debentures due 2031 Convertible Subordinated Debt Mentor Redemption period April 5, 2016	Jan. 31, 2012 4.00% Debentures due 2031 Convertible Subordinated Debt Redemption period April 1, 2018	Jan. 31, 2012 4.00% Debentures due 2031 Convertible Subordinated Debt Redemption period April 1, 2021	Jan. 31, 2012 4.00% Debentures due 2031 Convertible Subordinated Debt Redemption period April 1, 2026	Jan. 31, 2011 6.25% Debentures due 2026, issued 2006	Mar. 31, 2006 6.25% Debentures due 2026, issued 2006 Convertible Subordinated Debt	Jan. 31, 2012 6.25% Debentures due 2026, issued 2006 Convertible Subordinated Debt	Jan. 31, 2011 6.25% Debentures due 2026, issued 2006 Convertible Subordinated Debt	Jan. 31, 2010 6.25% Debentures due 2026, issued 2006 Convertible Subordinated Debt	Jan. 31, 2012 6.25% Debentures due 2026, issued fiscal 2011	Jan. 31, 2011 6.25% Debentures due 2026, issued fiscal 2011	Apr. 30, 2010 Term Loan due 2013	Jan. 31, 2012 Term Loan due 2013	Jan. 31, 2011 Term Loan due 2013	Nov. 30, 2009 Other Notes Payable
Debt Instrument [Line Items]
Loan expiration period, in years																		3 years
Maturity year			2031		2031						2026	2026					2026	2012		2012
Issued Debt					$ 253,000							$ 200,000				$ 31,509		$ 20,000
Term Loan, fixed principal amount																		500
Interest rate			4.00%		4.00%						6.25%	6.25%					6.25%				3.875%
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.
Other Notes Payable, due date																					Nov. 17, 2012
Debt effective interest rate						7.25%							8.60%	8.60%	8.60%
Redeemed amount of debt													196,509						18,500
Loss on early extinguishment of debt before tax	(3,518)	380											11,192						312
Effective interest rate, term loan																			4.81%
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%
Redemption period							Apr. 05, 2016	Apr. 01, 2018	Apr. 01, 2021	Apr. 01, 2026
Write-off of net unamortized debt discount													6,190
Premium on redemption													3,518
Write-off of unamortized debt issuance costs													$ 1,484