Investments Summary of Investment in Private Equity Funds (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Schedule of Equity Method Investments [Line Items]
Investment in private equity funds	$ 71,581	$ 76,581
Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Investment in private equity funds	26,985	36,551
ECP II [Member] | Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Investment in private equity funds	1,025	4,043
Discovery Fund [Member] | Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Investment in private equity funds	3,711	2,867
EMCP II [Member] | Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Investment in private equity funds	8,697	12,630
EMCP III [Member] | Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Investment in private equity funds	7,009	7,272
CSI Capital [Member] | Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Investment in private equity funds	265	3,030
Trilantic IV [Member] | Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Investment in private equity funds	3,321	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