Investments - Held-to-maturity Security - Narrative (Details) $ in Millions	9 Months Ended
Sep. 30, 2016 USD ($)
Schedule Of Held To Maturity Securities [Line Items]
Held-to-maturity debt security estimated unrealized holding gain	$ 46.8
LLC Note [Member]
Schedule Of Held To Maturity Securities [Line Items]
Debt instrument, interest rate, stated percentage	4.50%

Contractual interest rate for funds borrowed, under the debt agreement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Amount of unrecognized gain before loss on investments in held-to-maturity securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27232-111563

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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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