Commitments and Contingencies - Additional Information (Detail) - Claim	9 Months Ended	12 Months Ended
Sep. 30, 2017	Dec. 31, 2016
Indemnification Agreement [Member]
Loss Contingencies [Line Items]
Claims received by fund	0	0

The total number of new claims filed pertaining to a loss contingency during the period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14435-108349

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