Investments Summary of Investment in Private Equity Funds (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Schedule of Equity Method Investments [Line Items]
Investment in private equity funds	$ 76,581	$ 67,560
Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Investment in private equity funds	36,551	32,379
ECP II [Member] | Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Investment in private equity funds	4,043	3,251
Discovery Fund [Member] | Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Investment in private equity funds	2,867	5,015
EMCP II [Member] | Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Investment in private equity funds	12,630	11,125
EMCP III [Member] | Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Investment in private equity funds	7,272	3,852
CSI Capital [Member] | Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Investment in private equity funds	3,030	3,248
Trilantic IV [Member] | Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Investment in private equity funds	3,798	4,356
Trilantic V [Member] | Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Investment in private equity funds	$ 2,911	$ 1,532