Investments - Investments in Variable Interest Entities (Detail) (Variable Interest Entity, Not Primary Beneficiary, Aggregated Disclosure [Member], USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Variable Interest Entity, Not Primary Beneficiary, Aggregated Disclosure [Member]
Variable Interest Entity [Line Items]
Investment	$ 8,682	$ 15,199
Maximum Exposure to Loss	$ 25,662	$ 44,441