Fair Value - Valuation Technique and Inputs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Fair Value Inputs Assets Quantitative Information [Line Items]
Fixed maturities	$ 13,448,262	$ 13,918,745
Equities	443,861	1,056,514
Other invested assets carried at fair value	190,899	111,476
Funds held directly managed investments carried at fair value	399,899	472,593
Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Fixed maturities	508,546	599,646
Equities	37,556	40,134
Other invested assets carried at fair value	211,007	116,074
Funds held directly managed investments carried at fair value	10,146	13,530
U.S. states, territories and municipalities | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Fixed maturities	$ 138,847	$ 149,728
U.S. states, territories and municipalities | Minimum [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Credit spreads	1.20%	2.20%
U.S. states, territories and municipalities | Maximum [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Credit spreads	10.30%	10.10%
U.S. states, territories and municipalities | Weighted Average [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Credit spreads	4.10%	4.60%
Asset-backed securities [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Fixed maturities	$ 369,699	$ 449,918
Asset-backed securities [Member] | Minimum [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Credit spreads	4.10%	4.00%
Asset-backed securities [Member] | Maximum [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Credit spreads	11.40%	12.10%
Asset-backed securities [Member] | Weighted Average [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Credit spreads	7.70%	7.10%
Finance [Member] | Weighted market comparables [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Equities	$ 16,627	$ 14,561
Finance [Member] | Profitability Analysis [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Equities	$ 6,133	$ 5,792
Finance [Member] | Minimum [Member] | Weighted market comparables [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Net income multiple	14.4	19.0
Tangible book value multiple	1.5	1.3
Liquidity discount	25.00%	25.00%
Comparable return	7.90%	7.30%
Finance [Member] | Minimum [Member] | Profitability Analysis [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Projected Return On Equity	14.00%	14.00%
Finance [Member] | Maximum [Member] | Weighted market comparables [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Net income multiple	14.4	19.0
Tangible book value multiple	1.5	1.3
Liquidity discount	25.00%	25.00%
Comparable return	7.90%	7.30%
Finance [Member] | Maximum [Member] | Profitability Analysis [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Projected Return On Equity	14.00%	14.00%
Finance [Member] | Weighted Average [Member] | Weighted market comparables [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Net income multiple	14.4	19.0
Tangible book value multiple	1.5	1.3
Liquidity discount	25.00%	25.00%
Comparable return	7.90%	7.30%
Finance [Member] | Weighted Average [Member] | Profitability Analysis [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Projected Return On Equity	14.00%	14.00%
Technology [Member] | Weighted market comparables [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Equities	$ 8,207	$ 8,555
Technology [Member] | Minimum [Member] | Weighted market comparables [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Gross revenue/fair value	1.2	1.6
Technology [Member] | Maximum [Member] | Weighted market comparables [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Gross revenue/fair value	1.2	1.6
Technology [Member] | Weighted Average [Member] | Weighted market comparables [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Gross revenue/fair value	1.2	1.6
Technology [Member] | Minimum [Member] | Weighted market comparables [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Adjusted earnings multiple	8.4	10.2
Technology [Member] | Maximum [Member] | Weighted market comparables [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Adjusted earnings multiple	8.4	10.2
Technology [Member] | Weighted Average [Member] | Weighted market comparables [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Adjusted earnings multiple	8.4	10.2
Communications [Member] | Weighted market comparables [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Equities	$ 1,985	$ 2,640
Communications [Member] | Minimum [Member] | Weighted market comparables [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Adjusted earnings multiple	9.4	9.4
Comparable return	0.00%	(10.60%)
Communications [Member] | Maximum [Member] | Weighted market comparables [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Adjusted earnings multiple	9.4	9.4
Comparable return	0.00%	(10.60%)
Communications [Member] | Weighted Average [Member] | Weighted market comparables [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Adjusted earnings multiple	9.4	9.4
Comparable return	0.00%	(10.60%)
Total return swaps [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Other invested assets carried at fair value	$ (133)	$ (1,522)
Total return swaps [Member] | Minimum [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Credit spreads	3.00%	3.60%
Total return swaps [Member] | Maximum [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Credit spreads	29.30%	19.30%
Total return swaps [Member] | Weighted Average [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Credit spreads	16.50%	16.30%
Insurance-linked securities- longevity swaps [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Other invested assets carried at fair value	$ 9,428
Insurance-linked securities- longevity swaps [Member] | Minimum [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Credit spreads	2.40%
Insurance-linked securities- longevity swaps [Member] | Maximum [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Credit spreads	2.40%
Insurance-linked securities- longevity swaps [Member] | Weighted Average [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Credit spreads	2.40%
Notes and loan receivables [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Other invested assets carried at fair value	$ 10,415	$ 13,237
Notes and loan receivables [Member] | Minimum [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Credit spreads	17.50%	17.50%
Gross revenue/fair value	1.1	1.5
Notes and loan receivables [Member] | Maximum [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Credit spreads	17.50%	17.50%
Gross revenue/fair value	1.5	1.7
Notes and loan receivables [Member] | Weighted Average [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Credit spreads	17.50%	17.50%
Gross revenue/fair value	1.5	1.7
Notes and Loans Receivable 2 [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Other invested assets carried at fair value	$ 84,080	$ 8,068
Notes and Loans Receivable 2 [Member] | Minimum [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Credit spreads	6.00%	12.60%
Notes and Loans Receivable 2 [Member] | Maximum [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Credit spreads	26.80%	12.60%
Notes and Loans Receivable 2 [Member] | Weighted Average [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Credit spreads	7.40%	12.60%
Notes securitization [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Other invested assets carried at fair value	$ 31,427	$ 23,512
Notes securitization [Member] | Minimum [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Credit spreads	2.40%	3.50%
Notes securitization [Member] | Maximum [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Credit spreads	7.10%	6.60%
Notes securitization [Member] | Weighted Average [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Credit spreads	6.90%	6.40%
Annuities and residuals [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Other invested assets carried at fair value	$ 8,436	$ 13,243
Annuities and residuals [Member] | Minimum [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Credit spreads	5.10%	4.90%
Prepayment speed	0.00%	0.00%
Constant default rate	0.30%	0.30%
Annuities and residuals [Member] | Maximum [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Credit spreads	15.40%	9.60%
Prepayment speed	15.00%	15.00%
Constant default rate	17.50%	17.50%
Annuities and residuals [Member] | Weighted Average [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Credit spreads	12.70%	7.80%
Prepayment speed	2.10%	4.30%
Constant default rate	4.40%	6.30%
Private Equity-Direct [Member] | Discounted Cash Flow And Weighted Market Comparables [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Other invested assets carried at fair value	$ 8,792	$ 8,536
Private Equity-Direct [Member] | Minimum [Member] | Discounted Cash Flow And Weighted Market Comparables [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Net income multiple	9.2	9.0
Tangible book value multiple	1.9	2.0
Recoverability of intangible assets	0.000	0.000
Private Equity-Direct [Member] | Maximum [Member] | Discounted Cash Flow And Weighted Market Comparables [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Net income multiple	9.2	9.0
Tangible book value multiple	1.9	2.0
Recoverability of intangible assets	0.000	0.000
Private Equity-Direct [Member] | Weighted Average [Member] | Discounted Cash Flow And Weighted Market Comparables [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Net income multiple	9.2	9.0
Tangible book value multiple	1.9	2.0
Recoverability of intangible assets	0.000	0.000
Private equity funds [Member] | Reported market value | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Other invested assets carried at fair value	$ 29,222	$ 18,494
Private equity funds [Member] | Minimum [Member] | Reported market value | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Net asset value, as reported	100.00%	100.00%
Market adjustments	(4.90%)	(7.60%)
Private equity funds [Member] | Maximum [Member] | Reported market value | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Net asset value, as reported	100.00%	100.00%
Market adjustments	5.20%	11.00%
Private equity funds [Member] | Weighted Average [Member] | Reported market value | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Net asset value, as reported	100.00%	100.00%
Market adjustments	(0.50%)	(1.60%)
Private Equity - Other [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Other invested assets carried at fair value	$ 33,284	$ 32,842
Private Equity - Other [Member] | Minimum [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Effective Yield	5.80%	5.80%
Private Equity - Other [Member] | Maximum [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Effective Yield	5.80%	5.80%
Private Equity - Other [Member] | Weighted Average [Member] | Discounted cash flow [Member] | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Effective Yield	5.80%	5.80%
Other invested assets [Member] | Reported market value | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Funds held directly managed investments carried at fair value	$ 10,146	$ 13,398
Other invested assets [Member] | Minimum [Member] | Reported market value | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Net asset value, as reported	100.00%	100.00%
Market adjustments	(16.00%)	(15.40%)
Other invested assets [Member] | Maximum [Member] | Reported market value | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Net asset value, as reported	100.00%	100.00%
Market adjustments	0.00%	0.00%
Other invested assets [Member] | Weighted Average [Member] | Reported market value | Significant unobservable inputs (Level 3) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Net asset value, as reported	100.00%	100.00%
Market adjustments	(15.00%)	(14.50%)