Investment Securities (Significant Unobservable Inputs) (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2015 USD ($) Investment	Dec. 31, 2014 USD ($)	Jun. 30, 2015 input
Quantitative information for Level 3 Fair Value Measurements Assets
Number of Investments with Significant Unobseravble Inputs | Investment	1
Conditional Prepayment Rate	12.00%
Discount Yield [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Fair Value Inputs, Discount Rate
NR | Preferred Stock | Discounted cash flows
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 70,300,000	$ 71,100,000
NR | Preferred Stock | Discount Yield [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Fair Value Inputs, Discount Rate	8.40%	7.10%
NR | Convertible Preferred Stock [Member] | Multiple of EBITA [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Unobservable Inputs | input			0
Assets, Fair Value Disclosure	$ 5,600,000	$ 3,800,000
Share Price of Most Recent Transaction	6.00	6.00
NR | Convertible Preferred Stock [Member] | Recent transaction [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure		4,500,000
Share Price of Most Recent Transaction		0.71
NR | Seller Priority Surplus Note [Member] | Discounted cash flows
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 41,000,000	$ 44,000,000
Fair Value Inputs, Discount Rate	11.60%	9.30%
Timing of interest payments	5 years	5 years
Timing of principal payments	10 years	10 years
NR | Pari Passu Surplus Note [Member] | Discounted cash flows
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 17,000,000	$ 21,100,000
Fair Value Inputs, Discount Rate	18.30%	13.50%
Timing of interest payments	5 years	5 years
Timing of principal payments	15 years	10 years
CompareNow [Member] | NR | Private equity funds | Average Share Price
Quantitative information for Level 3 Fair Value Measurements Assets
Share Price of Most Recent Transaction	$ 1.06
Ironshore [Member] | NR | Private equity funds | Recent transaction [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	34,200,000	$ 39,500,000
Ironshore [Member] | NR | Private equity funds | Multiple of GAAP book value [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Share Price of Most Recent Transaction		1.10
Ironshore [Member] | NR | Private equity funds | Average Share Price
Quantitative information for Level 3 Fair Value Measurements Assets
Share Price of Most Recent Transaction	17.16
durchblicker.at [Member] | NR | Private equity funds | Recent transaction [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	9,600,000	10,400,000
Share Price of Most Recent Transaction	290.96	290.96
Centrus [Member] | NR | Debt securities issued by corporations | Discounted cash flows
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure		$ 5,300,000
Fair Value Inputs, Discount Rate		10.00%
PassportCard [Member] | NR | Private equity funds | Average Share Price
Quantitative information for Level 3 Fair Value Measurements Assets
Share Price of Most Recent Transaction	$ 1.00
Minimum | discount spread [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Basis points	0.45%
Minimum | Default Rate [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Constant Default Rate	2.50%
Maximum | discount spread [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Basis points	1.80%
Maximum | Default Rate [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Constant Default Rate	8.75%
Standard & Poor's, B Rating [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Basis points	2.50%
Standard & Poor's, CCC Rating [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Basis points	2.50%
PassportCard [Member] | NR | Private equity funds | Recent transaction [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 21,000,000
CompareNow [Member] | NR | Private equity funds | Recent transaction [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 20,100,000	$ 20,100,000
CompareNow [Member] | NR | Private equity funds | Average Share Price
Quantitative information for Level 3 Fair Value Measurements Assets
Share Price of Most Recent Transaction		$ 1.06