Investment Securities (Significant Unobservable Inputs) (Details)	6 Months Ended	12 Months Ended
	Jun. 30, 2015 USD ($) input Investment	Dec. 31, 2014 USD ($)
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	$ 71,200,000	$ 71,100,000
NR | Preferred Stock | Discount Yield [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Fair Value Inputs, Discount Rate	7.10%	7.10%
NR | Private equity funds | Multiple of GAAP book value [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 33,100,000	$ 40,200,000
Book Value Multiple to Calculate Fair Value	120.00%	110.00%
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
NR | Private equity funds | Share Price of Most Recent Transaction
Quantitative information for Level 3 Fair Value Measurements Assets
Share Price of Most Recent Transaction	$ 1.06	1.06
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	$ 4,500,000	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	$ 45,400,000	$ 44,000,000
Fair Value Inputs, Discount Rate	10.20%	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	$ 20,900,000	$ 21,100,000
Fair Value Inputs, Discount Rate	15.50%	13.50%
Timing of interest payments	5 years	5 years
Timing of principal payments	15 years	10 years
Standard & Poor's, A- Rating | Non-Agency Commercial Mortgage Backed Securities [Member] [Member] | Broker Pricing [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 7,400,000
durchblicker.at [Member] | NR | Private equity funds | Recent Transaction Two [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	9,500,000	$ 10,400,000
Share Price of Most Recent Transaction	290.96	290.96
BE Reinsurance [Member] | NR | Private equity funds | Recent Transaction Three [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	16,100,000	15,800,000
Share Price of Most Recent Transaction	$ 0.13	0.13
Centrus [Member] | NR | Debt securities issued by corporations | Discounted cash flows
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure		$ 5,600,000
Fair Value Inputs, Discount Rate		10.00%
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%