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Fair Value Measurement (Narrative) (Details) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2017 USD ($) Agreement	Dec. 31, 2016	Jun. 30, 2016 USD ($)
Credit Derivatives [Line Items]
Number of line of credit agreement | Agreement	2
Equity securities [Member]
Credit Derivatives [Line Items]
Transfer of equity securities from Level 2 to Level 1 | $	$ 35.4		$ 0.0
Standard & Poor's, BBB Rating [Member] | Corporate debt with limited observable inputs [Member]
Credit Derivatives [Line Items]
Credit rating	77.00%
NRSRO | Standard & Poor's, BBB+ Rating [Member] | Corporate debt with limited observable inputs [Member]
Credit Derivatives [Line Items]
Credit rating		84.00%

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-SubTopic 10
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