Fair Value Measurement of Assets on Recurring Basis (Detail) (Fair Value, Measurements, Recurring, USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Fair Value, Inputs, Level 1
Rabbi Trust
Mutual funds	$ 13,628	$ 13,349	$ 14,591
Equities	11,207	9,843	8,641
Total	24,835	23,192	23,232
Fair Value, Inputs, Level 2
Rabbi Trust
Common/collective trust funds	1,545	2,265	455
Total	$ 1,545	$ 2,265	$ 455

This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258

Name:	us-gaap_AssetsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant