Property, Equipment and Capitalized Software (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Equipment and Capitalized Software
Property, equipment and capitalized software, gross	$ 512,674	$ 142,844
Less: Accumulated depreciation and amortization	(375,656)	(113,184)
Total property, equipment and capitalized software, net	137,018	29,660
Depreciation expense	36,800	19,600	$ 24,000
Capitalized software costs
Property, Equipment and Capitalized Software
Property, equipment and capitalized software, gross	94,915	77,591
Leasehold improvements
Property, Equipment and Capitalized Software
Property, equipment and capitalized software, gross	93,624	3,636
Furniture, fixtures and equipment
Property, Equipment and Capitalized Software
Property, equipment and capitalized software, gross	$ 324,135	61,540
Land
Property, Equipment and Capitalized Software
Property, equipment and capitalized software, gross		$ 77

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.14)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 360
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-Section 50
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-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

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+ References

No definition available.

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Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
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-Subparagraph (SX 210.5-02(13))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
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-Section S99
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-Subparagraph (SX 210.7-03(a)(8))
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