Fair Value Disclosures (Investments Measured At Fair Value Based On Net Asset Value) (Additional Information) (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2015 USD ($) fund	Dec. 31, 2014 USD ($)
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Investments in managed funds	$ 604,831	$ 281,470
Equity Long/Short Hedge Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Amount redeemable	108,100
Investment in private asset management fund managed by company	$ 51,800	$ 117,200
Funds Of Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Percentage of investments with no redemption provisions	95.00%	95.00%
Estimated period for the liquidation of the underlying assets	16 months
Folger Hill Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Number of funds | fund	2
Notice period redemption of investments prior notice period	45 days
Investments in managed funds	$ 377,200
Equity Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Percentage of investments in certain industries	100.00%	99.00%
Multi-Strategy Fund [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fee to withdraw from fund	5.00%
Quarterly maximum withdrawal percentage	25.00%
Fixed Income and High Yield Hedge Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Percentage of funds being liquidated	7.00%	8.00%
Minimum [Member] | Equity Long/Short Hedge Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Notice period redemption of investments prior written notice period	30 days
Minimum [Member] | Equity Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated period for the liquidation of the underlying assets	1 year
Maximum [Member] | Equity Long/Short Hedge Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Notice period redemption of investments prior written notice period	90 days
Maximum [Member] | Equity Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated period for the liquidation of the underlying assets	8 years