Quarterly Financial Information (Narrative) (Details) - USD ($) $ in Thousands	Jul. 31, 2015	Apr. 30, 2015	Jan. 31, 2015	Jul. 31, 2014
Accounts receivable, less allowance	$ 460,027			$ 474,157
Inventories, net	264,955			253,351
Retained earnings	$ 815,166			$ 702,435
Effect of Revision [Member]
Accounts receivable, less allowance		$ 800	$ 8,400
Inventories, net		600	6,000
Retained earnings		$ 200	$ 1,600