Changes in Fair Value of Plans Level 3 Assets (Detail) (Pension Benefits, USD $) In Thousands, unless otherwise specified						12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010	Dec. 31, 2012 Unobservable inputs (Level 3)		Dec. 31, 2011 Unobservable inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, beginning balance	$ 563,303	[1]	$ 531,105	[1]	$ 507,064	$ 73,025	[1]	$ 69,399
Total gains relating to assets sold during the period						31	[2]	4,471	[2]
Total unrealized gains relating to assets still held at the reporting date						2,311	[2]	(6,367)	[2]
Purchases								25,000
Sales						(4,476)		(19,478)
Fair value of plan assets, Ending Balance	$ 563,303	[1]	$ 531,105	[1]	$ 507,064	$ 70,829	[1]	$ 73,025	[1]

[1] See Note 17 "Pension Plans and Other Postretirement Benefits" for further discussion on fair value measurements of our pension and postretirement assets.

[2] These gains (losses) are recognized in the consolidated balance sheets and are included as changes in plan assets in the tables above.