Cash, Cash Equivalents and Investments (Details 3) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2017	Dec. 31, 2016
Security Owned Not Readily Marketable [Line Items]
Carrying value of non-marketable investments	$ 3.2	$ 3.2
Cost-method investments [Member]
Security Owned Not Readily Marketable [Line Items]
Gain on sale of investment	$ 9.1

Aggregate carrying value of owned private equity or other securities for which a quoted market price is not readily determinable, the value of which has been determined by management based upon fair value methods, including pricing of similar securities and valuation techniques and is included in the schedule of financial condition or the balance sheet.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Rule 15c3-1
-Number 240
-Section 15c3-1

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