Cost and Market Value Associated with Assets Held in Merchandise Trusts (Parenthetical) (Detail) - Merchandise Trusts - Variable Interest Entity, Primary Beneficiary	6 Months Ended
Jun. 30, 2016
Minimum
Schedule of Available-for-sale Securities [Line Items]
Fixed income funds and equity funds, redemption period	30 days
Maximum
Schedule of Available-for-sale Securities [Line Items]
Fixed income funds and equity funds, redemption period	90 days

Period when redemption restriction has been in effect for investments for which net asset value per share is calculated (including by unit, membership interest, or other equity (ownership interest) unit measure), in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 6A
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=SL6742756-110258

Name:	us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareRedemptionRestrictionPeriodInEffect1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration