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Shareholders' Equity (Common Stock Buyback) (Details) - Common Stock Buyback - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity, Class of Treasury Stock [Line Items]
Shares repurchased and retired during period	6,744	4,403	6,600
Value of shares repurchased during period	$ 404,759	$ 248,114	$ 294,374

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

Number of shares that have been repurchased and retired during the period.

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Equity impact of the value of stock that has been repurchased during the period and has not been retired and is not held in treasury. Some state laws may mandate the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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