Goodwill and Intangible Assets - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Disposal Group, Including Discontinued Operation, Impairment of Intangible Assets		$ 15.0
Assets held for sale	$ 8.2	$ 26.0
Weighted average useful life	2 years	3 years
Minimum
Finite-Lived Intangible Assets [Line Items]
Amortization period	1 year
Maximum
Finite-Lived Intangible Assets [Line Items]
Amortization period	7 years
Trading rights
Finite-Lived Intangible Assets [Line Items]
Impairment charges	$ 0.7
Amortization period	4 years	5 years
Market Making
Finite-Lived Intangible Assets [Line Items]
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount	20.00%
Goodwill	$ 16.4	$ 16.4

Disposal Group, Including Discontinued Operation, Impairment of Intangible Assets

No definition available.

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- Definition

Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 1
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- Definition

Amount classified as assets attributable to disposal group held for sale or disposed of.

+ References

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- Definition

Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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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.

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No definition available.

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- Definition

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

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- Definition

The amount of impairment loss recognized in the period resulting from the write-down of the carrying amount of a finite-lived intangible asset to fair value.

+ References

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-Publisher FASB
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- Definition

Percentage of fair value of reporting unit in excess of carrying amount.

+ References

No definition available.

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