Fair Value of Assets and Liabilities - (Increases)/decreases in fair value and locations related to liabilities measured at fair value on a recurring basis (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Cost of revenue (FCR liability)
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items]
(Increase)/decrease in liabilities	$ (19,226)	$ (11,980)	$ (40,736)	$ (25,449)
Other gains/(losses) (Servicing liabilities)
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings [Line Items]
(Increase)/decrease in liabilities	$ (85)	$ 0	$ (201)	$ 0

Amount of gain (loss) recognized on the income statement for financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration