Investment Securities (Significant Unobservable Inputs) (Details) - Standard Poors NR Rating - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Private equity funds
Quantitative information for Level 3 Fair Value Measurements Assets
Unobservable Inputs		0.21
Time until expiration of security	4 years	4 years
Volatility Rate	50.00%	50.00%
Risk Free Rate	1.77%	1.00%
Private equity funds \| Share price of most recent transaction
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 21.0
Unobservable Inputs	1
Private equity funds \| Discounted cash flow/ Option pricing method
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 11.3	$ 9.3
Unobservable Inputs	0.21
Convertible Preferred Stock \| Share price of most recent transaction
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 3.6
Unobservable Inputs	2.521
Convertible Preferred Stock \| Discounted cash flow
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 14.5
Unobservable Inputs	2.06
Convertible Preferred Stock \| Multiple of EBITDA
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value		$ 3.6
Unobservable Inputs		6.0
Investment A \| Private equity funds \| Share price of most recent transaction
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value		$ 21.0
Unobservable Inputs		1.00
Investment B \| Private equity funds \| Share price of most recent transaction
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value		$ 22.1
Unobservable Inputs		.68
Investment B \| Private equity funds \| Discounted cash flow
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 22.1
Unobservable Inputs	.68
Investment C \| Private equity funds \| Share price of most recent transaction
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value		$ 3.2
Unobservable Inputs		2.52
Investment E \| Convertible Preferred Stock \| Share price of most recent transaction
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value		$ 27.0
Unobservable Inputs		3.83
Investment E \| Convertible Preferred Stock \| Multiple of EBITDA
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 0.6
Unobservable Inputs	6

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
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-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Topic 820
-SubTopic 10
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