Related Party Transactions (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Advisory fees from affiliate	$ 21,034	$ 20,828	$ 63,729	$ 58,745
Receivable for advisory and service fees, from affiliates	16,451		16,451		16,245	[1]
Affiliated Entity [Member]
Advisory fees from affiliate	16,400	16,500	50,300	46,500
Receivable for advisory and service fees, from affiliates	$ 16,500		$ 16,500		$ 16,200

[1] Derived from the audited consolidated financial statements at December 31, 2011.