Marketable Securities - Securitization Trusts (Details) - Securitization Trust, Primary Beneficiary - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
Jun. 30, 2018	Dec. 31, 2017
Securitization Trust [Line Items]
Size/principal outstanding	$ 2,642,768	$ 2,714,823
Assets on Balance Sheet	7,120	11,794
Liabilities on Balance Sheet	0	0
Maximum exposure to loss	7,120	11,794
Year-To-Date loss on sale	0	0
Year-To-Date cash flows	$ 858	$ 3,193

Variable Interest Entity, Consolidated, Aggregate Loss on Sale

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- Definition

Variable Interest Entity, Consolidated, Aggregate Principal of Underlying Assets

+ References

No definition available.

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- Definition

Variable Interest Entity, Consolidated, Cash Flows from Variable Interest Entity

+ References

No definition available.

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- Definition

The carrying amount of the consolidated Variable Interest Entity's assets included in the reporting entity's statement of financial position.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
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-Section 50
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- Definition

The carrying amount of the consolidated Variable Interest Entity's liabilities included in the reporting entity's statement of financial position.

+ References

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- Definition

The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 6
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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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