Summary of Significant Accounting Policies - Software and Website Development Costs Narrative (Details) - USD ($)	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Technology and development
Property, Plant and Equipment [Line Items]
Capitalized software costs write off amount	$ 0
Software and Software Development Costs
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Capitalized software costs	$ 50,400,000	$ 86,000,000.0
Accumulated amortization of computer software	28,200,000	62,200,000
Acceleration of amortization	$ 1,100,000	1,000,000.0
Software and Software Development Costs, Assets Not Yet Placed in Service
Property, Plant and Equipment [Line Items]
Accumulated amortization written off		0
Acceleration of amortization		$ 0

Represents the amount of accelerated amortization related to certain assets written off during the period.

No definition available.

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- Definition

Amount of decrease in accumulated depreciation, depletion and amortization as a result of sale or disposal of property, plant and equipment.

+ References

No definition available.

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- Definition

For each balance sheet presented, the amount of accumulated amortization for capitalized computer software costs.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 985
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6501960&loc=d3e128462-111756

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- Definition

Amount before accumulated amortization of capitalized costs for computer software, including but not limited to, acquired and internally developed computer software.

+ References

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- Definition

Amount of impairment loss from capitalized computer software costs.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 985
-SubTopic 20
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6501960&loc=d3e128487-111756

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 985
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)(2)
-URI http://asc.fasb.org/extlink&oid=6501960&loc=d3e128462-111756

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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.

+ Details

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- Definition

Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

+ References

No definition available.

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