Combined Funded Status of Plans and their Reconciliation with Related Amounts Recognized in Consolidated Financial Statements(Pension Plans) (Detail) (USD $)	1 Months Ended	12 Months Ended
	Apr. 30, 2011	Dec. 31, 2012 Pension Plans, Defined Benefit		Dec. 31, 2011 Pension Plans, Defined Benefit		Dec. 31, 2010 Pension Plans, Defined Benefit
Change in Benefit Obligation
Projected benefit obligation at beginning of year		$ 867,374,000		$ 761,384,000
Service cost		22,349,000		20,762,000		19,217,000
Interest cost		43,194,000		42,383,000		41,621,000
Plan amendment		1,286,000	[1]	0	[1]
Actuarial loss		96,222,000		81,699,000
Benefits paid		(39,087,000)		(38,854,000)
Projected benefit obligation at end of year		991,338,000		867,374,000		761,384,000
Change in Plan Assets
Fair value of assets at beginning of year		636,648,000		630,303,000
Actual return on plan assets	10,814,000	81,021,000		40,293,000
Employer contribution		4,509,000		4,906,000		78,359,000
Benefits paid		(39,087,000)		(38,854,000)
Fair value of assets at end of year		683,091,000		636,648,000		630,303,000
Funded status		(308,247,000)		(230,726,000)
Net amount recognized		(308,247,000)		(230,726,000)
Amounts Recognized in the Consolidated Balance Sheets
Current liabilities		(5,211,000)		(4,880,000)
Noncurrent liabilities		(303,036,000)		(225,846,000)
Net amount recognized		(308,247,000)		(230,726,000)
Amounts Recognized in Accumulated Other Comprehensive Income
Net actuarial loss		325,807,000		281,352,000
Prior service cost		1,609,000		597,000
Total amount recognized		$ 327,416,000		$ 281,949,000

[1] An amendment to the salaried plan was necessary to maintain compliance with required discrimination testing.