Pension and Postretirement Benefits - Additional Information (Detail)	9 Months Ended
Sep. 30, 2015 USD ($)
SERP Plans
Defined Benefit Plan Disclosure [Line Items]
Estimated contribution of pension plans	$ 53,725,000

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_DefinedBenefitPlanDisclosureLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration