Bank Revolving Credit Facility (Details) (USD $) In Thousands, unless otherwise specified	Jan. 31, 2013		Jan. 31, 2012
Debt Disclosure [Abstract]
Maximum borrowings	$ 450,000	[1]	$ 450,000	[1]
Borrowings	0		0
Letters of credit	67,456		69,389
Surety Bonds	0		0
Available credit	$ 382,544		$ 380,611

[1] The maximum borrowings under the Credit Facility was increased to $465,000,000 on February 21, 2013, upon entering into the fourth amendment to the Credit Facility, as discussed below.