Reconciliation of Fair Value Measurements of Pension Plan Assets Using Significant Unobservable Inputs ( Level 3) (Detail) (Pension Plans, Defined Benefit, USD $)								12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Debt Securities	Dec. 31, 2011 Debt Securities	Dec. 31, 2012 Venture Capital And Partnerships	Dec. 31, 2011 Venture Capital And Partnerships	Dec. 31, 2012 Fair Value, Inputs, Level 3		Dec. 31, 2011 Fair Value, Inputs, Level 3		Dec. 31, 2012 Fair Value, Inputs, Level 3 Debt Securities		Dec. 31, 2011 Fair Value, Inputs, Level 3 Debt Securities		Dec. 31, 2012 Fair Value, Inputs, Level 3 Venture Capital And Partnerships		Dec. 31, 2011 Fair Value, Inputs, Level 3 Venture Capital And Partnerships
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value of assets at beginning of year	$ 683,091,000	$ 636,648,000	$ 630,303,000	$ 155,874,000	$ 152,240,000	$ 98,011,000	$ 106,801,000	$ 106,801,000	[1]	$ 96,552,000		$ 0	[1]	$ 308,000		$ 106,801,000	[1]	$ 96,244,000
Actual return on plan assets
Relating to assets still held								(6,858,000)		13,696,000		0		0		(6,858,000)		13,696,000
Relating to assets sold								0		0		0		0		0		0
Purchases, sales and settlements, net								15,356,000		(3,139,000)		0		0		15,356,000		(3,139,000)
Transfers in (out) of Level 3								(17,288,000)		(308,000)		0		(308,000)		(17,288,000)		0
Fair value of assets at end of year	$ 683,091,000	$ 636,648,000	$ 630,303,000	$ 155,874,000	$ 152,240,000	$ 98,011,000	$ 106,801,000	$ 98,011,000	[1]	$ 106,801,000	[1]	$ 0	[1]	$ 0	[1]	$ 98,011,000	[1]	$ 106,801,000	[1]

[1] See Note 1 under the caption Fair Value Measurements for a description of the fair value hierarchy.