Investments Summary of Investment in Private Equity Funds (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Schedule of Equity Method Investments [Line Items]
Investment in private equity funds	$ 68,733	$ 76,581
Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Investment in private equity funds	28,056	36,551
ECP II [Member] | Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Investment in private equity funds	1,017	4,043
Discovery Fund [Member] | Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Investment in private equity funds	5,830	2,867
EMCP II [Member] | Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Investment in private equity funds	8,088	12,630
EMCP III [Member] | Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Investment in private equity funds	6,791	7,272
CSI Capital [Member] | Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Investment in private equity funds	11	3,030
Trilantic IV [Member] | Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Investment in private equity funds	3,362	3,798
Trilantic V [Member] | Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Investment in private equity funds	$ 2,957	$ 2,911