Stockholders' Equity Stock Repurchase Program (Details) - USD ($) $ in Millions	Apr. 30, 2016	Jan. 31, 2016	Mar. 21, 2014
2014 Program [Member]
Share Repurchase [Line Items]
Stock Repurchase Program, Authorized Amount			$ 300.0
Stock Repurchase Program, Remaining Authorized Repurchase Amount		$ 58.6
2016 Program [Member]
Share Repurchase [Line Items]
Stock Repurchase Program, Authorized Amount	$ 500.0
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 415.9