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Notes Payable - Additional Information (Detail)
$ / shares in Units, $ in Thousands
3 Months Ended
Sep. 09, 2015
Feb. 25, 2015
Apr. 30, 2011
USD ($)
$ / shares
shares
Apr. 30, 2016
USD ($)
day
$ / shares
shares
Apr. 30, 2015
Jan. 31, 2016
USD ($)
Debt Instrument            
Notes payable (Note 6)       $ 242,037   $ 240,076
4.00% Debentures due 2031            
Debt Instrument            
Notes payable (Note 6)       236,849   $ 234,888
4.00% Debentures due 2031 | Convertible Subordinated Debt            
Debt Instrument            
Debt Instrument, Maturity Date, Description     2031      
Issued debt     $ 253,000      
Interest rate     4.00%      
Principal amount multiple     $ 1 $ 1    
Conversion rate | shares     48.6902 49.8058    
Conversion price | $ / shares     $ 20.54 $ 20.08    
Market price of common stock exceeding percent of the conversion price       120.00%    
Debt instrument conversion circumstance stock price | $ / shares       $ 24.09    
Debt instrument threshold trading days | day       20    
Debt instrument threshold consecutive trading days       30 days    
Market price of debentures declining to maximum percent of the value of the common stock       98.00%    
Amortization end date       2018-03    
Debt Instrument, Interest Rate During Period       7.25% 7.25%  
February 2015, Other Notes Payable [Member]            
Debt Instrument            
Notes payable (Note 6)       $ 3,188    
Interest rate   4.00%        
Debt Instrument, Maturity Date   Feb. 25, 2019        
September 2015, Other Notes Payable [Member]            
Debt Instrument            
Notes payable (Note 6)       $ 2,000    
Interest rate 4.00%          
Debt Instrument, Maturity Date Sep. 08, 2018          
Holder optional redemption on April 1, 2018 | 4.00% Debentures due 2031 | Convertible Subordinated Debt            
Debt Instrument            
Debentures redemption price       100.00%    
Holder optional redemption on April 1, 2021 | 4.00% Debentures due 2031 | Convertible Subordinated Debt            
Debt Instrument            
Debentures redemption price       100.00%    
Holder optional redemption on April 1, 2026 | 4.00% Debentures due 2031 | Convertible Subordinated Debt            
Debt Instrument            
Debentures redemption price       100.00%