Business Information - Additional Information (Detail)	12 Months Ended
Dec. 31, 2012 Segment Entity	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting Disclosure [Line Items]
Number of business segments	1
Number of principal sources of revenue	2
Advisory revenues as a percentage of total revenue	102.00%	103.00%	91.00%
Advisory revenues
Segment Reporting Disclosure [Line Items]
Number of clients that accounted for more than 10% of total revenues	0	0	0
Investment Revenues [Member]
Segment Reporting Disclosure [Line Items]
Number of individual investments accounting for more than 10% of total revenues	0	0	0

Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

No definition available.

Name:	us-gaap_NumberOfOperatingSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration