Shareholders' Equity Share-Repurchase Programs (Details) - Shares Approved December 2016 [Member] $ in Thousands	Mar. 31, 2018 USD ($)
Share-Repurchase Programs [Line Items]
Stock Repurchase Program, Authorized Amount	$ 400,000
Stock Repurchase Program, Dollar Value of Shares Repurchased	81,361
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 318,639

Amount remaining of a stock repurchase plan authorized.

No definition available.

Name:	us-gaap_StockRepurchaseProgramRemainingAuthorizedRepurchaseAmount1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant