Investments (Gains (Losses) Related to Trading Securities) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Investments, Debt and Equity Securities [Abstract]
Net (losses) gains recognized during the period	$ (1,829)	$ 9,052	$ 14,436	$ 17,678
Less: net gains (losses) recognized during the period on trading securities sold during the period	311	1,411	12,850	(11,285)
Unrealized (losses) gains recognized during the period on trading securities held	$ (2,140)	$ 7,641	$ 1,586	$ 28,963

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- Definition

The sum of the realized and unrealized net gain (loss) on trading securities during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27476-111563

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- Definition

Amount of gain (loss) realized from securities classified as trading.

+ References

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- Definition

Amount of unrealized holding gain (loss) recognized in the income statement for 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 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.7(c))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 35
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82895926&loc=d3e24584-111560

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563

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