Stockholders' Equity Stock Repurchase Program (Details) - 2016 Program [Member] - USD ($) $ in Millions	3 Months Ended
	Apr. 30, 2018	May 22, 2018
Share Repurchase [Line Items]
Stock Repurchase Program, Authorized Amount	$ 500.0
Stock Repurchase Program Expiration Date	Jan. 31, 2019
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 170.8
Subsequent Event [Member]
Share Repurchase [Line Items]
Stock Repurchase Program, Remaining Authorized Repurchase Amount		$ 160.0