Pension (Components Of Net Periodic Benefit Cost) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 1,333	$ 1,201
Interest Cost	1,794	1,776
Expected Return On Plan Assets	(2,412)	(2,349)
Amortization Of Prior Service Cost	6	6
Amortization Of Transition Obligation	0	0
Amortization Of Net Actuarial (Gain) Or Loss	757	805
Net Periodic Postretirement Benefit Cost	1,478	1,439
Estimated Contributions, Next Fiscal Year			365
Contributions	91
Estimated Contributions, Current Fiscal Year	274
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	337	272
Interest Cost	217	201
Expected Return On Plan Assets	0	0
Amortization Of Prior Service Cost	29	29
Amortization Of Transition Obligation	2	28
Amortization Of Net Actuarial (Gain) Or Loss	42	16
Net Periodic Postretirement Benefit Cost	627	546
Estimated Contributions, Next Fiscal Year			621
Contributions	155
Estimated Contributions, Current Fiscal Year	466
SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	313	34
Interest Cost	102	75
Expected Return On Plan Assets	0	0
Amortization Of Prior Service Cost	55	28
Amortization Of Transition Obligation	0	0
Amortization Of Net Actuarial (Gain) Or Loss	56	54
Net Periodic Postretirement Benefit Cost	$ 526	$ 191