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Fair Value Measurement (Narrative) (Details) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2015 USD ($) broker | Dec. 31, 2014 USD ($)
Fair Value Measurement [Line Items] |  |
Percentage of portfolio of unadjusted fair values obtained | 99.70% |
Percentage of portfolio of specific unadjusted broker quotes obtained | 0.30% |
Fair value of assets measured on a recurring basis | $ 3,380,642 | $ 3,403,822
Level 3 [Member] |  |
Fair Value Measurement [Line Items] |  |
Fair value of assets measured on a recurring basis | 10,431 | 11,719
Level 2 [Member] |  |
Fair Value Measurement [Line Items] |  |
Fair value of assets measured on a recurring basis | 2,892,014 | 2,649,217
Level 2 [Member] | Commercial Mortgage Backed Securities [Member] |  |
Fair Value Measurement [Line Items] |  |
Trading securities, fair value disclosure | $ 37,300 | $ 32,500
Minimum [Member] |  |
Fair Value Measurement [Line Items] |  |
Number of knowledgeable outside security brokers consulted to determine fair value | broker | 1 |

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- Definition Amount of investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=49167202&loc=d3e26626-111562 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.4) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=49167202&loc=d3e26610-111562 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Trading Securities -URI http://asc.fasb.org/extlink&oid=6526789 + Details
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