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Fair Value Measurement (Narrative) (Details) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2017 USD ($) Agreement | Dec. 31, 2016 USD ($)
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 | $ | $ 35,400,000 | $ 0
Standard & Poor's, BBB Rating [Member] | Corporate debt with limited observable inputs [Member] |  |
Credit Derivatives [Line Items] |  |
Credit rating | 88.00% |
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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- Definition Amount of transfers of assets measured on a recurring basis out of Level 2 of the fair value hierarchy into Level 1. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bb) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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