This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.12)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 323

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=16385135&loc=d3e33749-111570

Name:	us-gaap_EquityMethodInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Investments Summary of Other Equity Investments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Dec. 31, 2008
Schedule of Equity Method Investments [Line Items]
Investment in private equity funds	$ 62,223	$ 69,320
G5 [Member]
Schedule of Equity Method Investments [Line Items]
Investment in private equity funds	17,991	19,720
ABS [Member]
Schedule of Equity Method Investments [Line Items]
Investment in private equity funds	44,232	46,851
Pan [Member]
Schedule of Equity Method Investments [Line Items]
Investment in private equity funds	$ 0	$ 2,749	$ 4,158