Investments - Level III Investments (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Investments By Valuation Methodology Of Underlying Securities [Line Items]
Total Investments	$ 2,134,061	$ 2,138,096
Private Equity Segment [Member] | AAA Investments [Member]
Investments By Valuation Methodology Of Underlying Securities [Line Items]
Discounted cash flow models	1,617,445	1,581,975
Listed quotes	48,579	22,029
Total Investments	1,666,024	1,604,004
Other net (liabilities) assets	(6,931)	62,444
Total Net Assets	$ 1,659,093	$ 1,666,448
Discounted cash flow models	97.10%	98.60%
Listed quotes	2.90%	1.40%
Total Investments	100.00%	100.00%