Segment Reporting - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2012 Segment
Operating Statistics [Line Items]
Number of reportable segments	4
Date of acquisition of AlpInvest	July 1, 2011
Noncontrolling interest in AlpInvest [Member]
Operating Statistics [Line Items]
Percentage of equity interest of acquisition	60.00%
Percentage of economic interest	60.00%
Claren Road [Member] | Emerging Sovereign Group LLC [Member]
Operating Statistics [Line Items]
Percentage of economic interest	55.00%