Balance Sheet Accounts and Supplemental Disclosures - Redeemable Common Stock (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended	12 Months Ended
Dec. 31, 2015	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Nov. 30, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Payments for Repurchase of Equity	$ 0.2	$ 3.5	$ 6.2	$ 3.9	$ 6.7

The cash outflow to reacquire common and preferred stock.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3291-108585

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