Summary of Investment in Private Equity Funds (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Schedule of Equity Method Investments [Line Items]
Total Private Equity Funds	$ 63,957	$ 69,320
Private Equity Funds
Schedule of Equity Method Investments [Line Items]
Total Private Equity Funds	28,549	26,578
ECP II | Private Equity Funds
Schedule of Equity Method Investments [Line Items]
Total Private Equity Funds	3,830	3,793
Discovery Fund | Private Equity Funds
Schedule of Equity Method Investments [Line Items]
Total Private Equity Funds	3,534	3,060
EMCP II | Private Equity Funds
Schedule of Equity Method Investments [Line Items]
Total Private Equity Funds	10,887	10,400
EMCP III | Private Equity Funds
Schedule of Equity Method Investments [Line Items]
Total Private Equity Funds	2,603	1,696
CSI Capital | Private Equity Funds
Schedule of Equity Method Investments [Line Items]
Total Private Equity Funds	3,035	3,056
Trilantic IV | Private Equity Funds
Schedule of Equity Method Investments [Line Items]
Total Private Equity Funds	$ 4,660	$ 4,573