Notes Payable (Details) - USD ($) $ in Thousands	Apr. 30, 2016	Jan. 31, 2016
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
Notes Payable, Other Payables
Debt Instrument
Notes payable (Note 6)	$ 5,188	$ 5,188

Carrying value as of the balance sheet date of notes payable (with maturities initially due after one year or beyond the operating cycle if longer), excluding current portion.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_LongTermNotesPayable
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant