Investments - Summary of Investment in Private Equity Funds (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Schedule of Equity Method Investments [Line Items]
Total Private Equity Funds	$ 62,818	$ 69,320
Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Total Private Equity Funds	30,706	26,578
ECP II [Member] | Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Total Private Equity Funds	3,332	3,793
Discovery Fund [Member] | Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Total Private Equity Funds	4,594	3,060
EMCP II [Member] | Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Total Private Equity Funds	11,474	10,400
EMCP III [Member] | Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Total Private Equity Funds	3,419	1,696
CSI Capital [Member] | Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Total Private Equity Funds	3,210	3,056
Trilantic IV [Member] | Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Total Private Equity Funds	$ 4,677	$ 4,573