Shareholders' Equity Share-Repurchase Programs (Details) $ in Thousands	Sep. 30, 2017 USD ($)
Share-Repurchase Programs [Line Items]
Stock Repurchase Program, Authorized Amount	$ 800,000
Stock Repurchase Program, Dollar Value of Shares Repurchased	416,081
Stock Repurchase Program, Remaining Authorized Repurchase Amount	383,919
Shares Approved September 2015 [Member]
Share-Repurchase Programs [Line Items]
Stock Repurchase Program, Authorized Amount	400,000
Stock Repurchase Program, Dollar Value of Shares Repurchased	400,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount	0
Shares Approved December 2016 [Member]
Share-Repurchase Programs [Line Items]
Stock Repurchase Program, Authorized Amount	400,000
Stock Repurchase Program, Dollar Value of Shares Repurchased	16,081
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 383,919