Investments - Fair Value Option (Details) - Fair Value Option [Member] $ in Thousands	6 Months Ended
Jun. 30, 2018 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items] (Deprecated 2018-01-31)
Investments, fair value disclosure	$ 108,452
Net Gains and Losses Recognized During the Period	2,861
Less Net Gains and Losses Recognized due to Sales	0
Total Changes in Fair Values Included in Current-Period Earnings	2,861
Level 1 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items] (Deprecated 2018-01-31)
Investments, fair value disclosure	0
Level 2 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items] (Deprecated 2018-01-31)
Investments, fair value disclosure	108,452
Level 3 [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items] (Deprecated 2018-01-31)
Investments, fair value disclosure	$ 0

Fair Value, Option, Gain (Loss) Recognized

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- Definition

Fair Value, Option, Gain (Loss) Recognized Due To Sales

+ References

No definition available.

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- Definition

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.

+ References

No definition available.

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- Definition

For each line item in the statement of financial position, the amounts of gains and losses from fair value changes included in earnings.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 30
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14172-108612

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- Definition

Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

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