Assets and Liabilities Related to Interest in Non-Consolidated VIEs and Maximum Exposure to Loss (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Variable Interest Entity [Line Items]
Investments	$ 514,451	$ 364,709
Accounts Receivable	74,300	1,885
Due from Affiliates	68,521	112,686
Total VIE Assets	657,272	479,280
Due to Affiliates	308	2,657
Potential Clawback Obligation	54,393	36,040
Maximum Exposure to Loss	$ 711,973	$ 517,977