The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=6382943&loc=d3e33918-111571

Name:	us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Non-Controlling Interests in Consolidated Entities - Additional Information (Detail) - shares	Jun. 30, 2015	Jun. 05, 2015	Mar. 31, 2014	Mar. 10, 2014	Dec. 31, 2013
Noncontrolling Interest [Line Items]
Number of common units issued in public offering (in shares)	7,000,000	7,000,000	13,800,000	13,800,000
AlpInvest
Noncontrolling Interest [Line Items]
Equity interest acquired (as a percent)					40.00%