Commitments and Contingencies - Investigations (Details) $ in Millions	Sep. 30, 2018 USD ($)
Investigations by U.S. Securities and Exchange Commission (SEC) and U.S. Department of Justice (DOJ) \| Pending Litigation
Loss Contingencies [Line Items]
Estimated legal reserve	$ 12.0

Amount of loss contingency liability.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14326-108349

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