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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 |

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