Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified																																																																																											12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 OPEB [Member]	Dec. 31, 2011 OPEB [Member]	Dec. 31, 2010 OPEB [Member]	Dec. 31, 2012 Pension Plan [Member]	Dec. 31, 2011 Pension Plan [Member]	Dec. 31, 2010 Pension Plan [Member]	Dec. 31, 2012 Pension Plan [Member] Fair Value, Inputs, Level 1 [Member]	Dec. 31, 2011 Pension Plan [Member] Fair Value, Inputs, Level 1 [Member]	Dec. 31, 2012 Pension Plan [Member] Fair Value, Inputs, Level 2 [Member]	Dec. 31, 2011 Pension Plan [Member] Fair Value, Inputs, Level 2 [Member]	Dec. 31, 2012 Pension Plan [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2011 Pension Plan [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2012 Pension Plan [Member] Cash and Cash Equivalents [Member]	Dec. 31, 2011 Pension Plan [Member] Cash and Cash Equivalents [Member]	Dec. 31, 2012 Pension Plan [Member] Cash and Cash Equivalents [Member] Fair Value, Inputs, Level 1 [Member]	Dec. 31, 2011 Pension Plan [Member] Cash and Cash Equivalents [Member] Fair Value, Inputs, Level 1 [Member]	Dec. 31, 2012 Pension Plan [Member] Cash and Cash Equivalents [Member] Fair Value, Inputs, Level 2 [Member]	Dec. 31, 2011 Pension Plan [Member] Cash and Cash Equivalents [Member] Fair Value, Inputs, Level 2 [Member]	Dec. 31, 2012 Pension Plan [Member] Cash and Cash Equivalents [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2011 Pension Plan [Member] Cash and Cash Equivalents [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2012 Pension Plan [Member] U.S. Government Obligations [Member]	Dec. 31, 2011 Pension Plan [Member] U.S. Government Obligations [Member]	Dec. 31, 2012 Pension Plan [Member] U.S. Government Obligations [Member] Fair Value, Inputs, Level 1 [Member]	Dec. 31, 2011 Pension Plan [Member] U.S. Government Obligations [Member] Fair Value, Inputs, Level 1 [Member]	Dec. 31, 2012 Pension Plan [Member] U.S. Government Obligations [Member] Fair Value, Inputs, Level 2 [Member]	Dec. 31, 2011 Pension Plan [Member] U.S. Government Obligations [Member] Fair Value, Inputs, Level 2 [Member]	Dec. 31, 2012 Pension Plan [Member] U.S. Government Obligations [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2011 Pension Plan [Member] U.S. Government Obligations [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2012 Pension Plan [Member] Corporate and Other Obligations [Member]	Dec. 31, 2011 Pension Plan [Member] Corporate and Other Obligations [Member]	Dec. 31, 2012 Pension Plan [Member] Corporate and Other Obligations [Member] Fair Value, Inputs, Level 1 [Member]	Dec. 31, 2011 Pension Plan [Member] Corporate and Other Obligations [Member] Fair Value, Inputs, Level 1 [Member]	Dec. 31, 2012 Pension Plan [Member] Corporate and Other Obligations [Member] Fair Value, Inputs, Level 2 [Member]	Dec. 31, 2011 Pension Plan [Member] Corporate and Other Obligations [Member] Fair Value, Inputs, Level 2 [Member]	Dec. 31, 2012 Pension Plan [Member] Corporate and Other Obligations [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2011 Pension Plan [Member] Corporate and Other Obligations [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2012 Pension Plan [Member] Common Stock [Member]	Dec. 31, 2011 Pension Plan [Member] Common Stock [Member]	Dec. 31, 2012 Pension Plan [Member] Common Stock [Member] Fair Value, Inputs, Level 1 [Member]	Dec. 31, 2011 Pension Plan [Member] Common Stock [Member] Fair Value, Inputs, Level 1 [Member]	Dec. 31, 2012 Pension Plan [Member] Common Stock [Member] Fair Value, Inputs, Level 2 [Member]	Dec. 31, 2011 Pension Plan [Member] Common Stock [Member] Fair Value, Inputs, Level 2 [Member]	Dec. 31, 2012 Pension Plan [Member] Common Stock [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2011 Pension Plan [Member] Common Stock [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2012 Pension Plan [Member] Commingled Funds [Member]	Dec. 31, 2011 Pension Plan [Member] Commingled Funds [Member]	Dec. 31, 2012 Pension Plan [Member] Commingled Funds [Member] Fair Value, Inputs, Level 1 [Member]	Dec. 31, 2011 Pension Plan [Member] Commingled Funds [Member] Fair Value, Inputs, Level 1 [Member]	Dec. 31, 2012 Pension Plan [Member] Commingled Funds [Member] Fair Value, Inputs, Level 2 [Member]	Dec. 31, 2011 Pension Plan [Member] Commingled Funds [Member] Fair Value, Inputs, Level 2 [Member]	Dec. 31, 2012 Pension Plan [Member] Commingled Funds [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2011 Pension Plan [Member] Commingled Funds [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2011 Pension Plan [Member] Common/Collective Trust Funds [Member]	Dec. 31, 2011 Pension Plan [Member] Common/Collective Trust Funds [Member] Fair Value, Inputs, Level 1 [Member]	Dec. 31, 2011 Pension Plan [Member] Common/Collective Trust Funds [Member] Fair Value, Inputs, Level 2 [Member]	Dec. 31, 2011 Pension Plan [Member] Common/Collective Trust Funds [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2012 Pension Plan [Member] Interest in Registered Investment Companies [Member]	Dec. 31, 2011 Pension Plan [Member] Interest in Registered Investment Companies [Member]	Dec. 31, 2012 Pension Plan [Member] Interest in Registered Investment Companies [Member] Fair Value, Inputs, Level 1 [Member]	Dec. 31, 2011 Pension Plan [Member] Interest in Registered Investment Companies [Member] Fair Value, Inputs, Level 1 [Member]	Dec. 31, 2012 Pension Plan [Member] Interest in Registered Investment Companies [Member] Fair Value, Inputs, Level 2 [Member]	Dec. 31, 2011 Pension Plan [Member] Interest in Registered Investment Companies [Member] Fair Value, Inputs, Level 2 [Member]	Dec. 31, 2012 Pension Plan [Member] Interest in Registered Investment Companies [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2011 Pension Plan [Member] Interest in Registered Investment Companies [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2012 Pension Plan [Member] Interest in Limited Partnerships [Member]	Dec. 31, 2011 Pension Plan [Member] Interest in Limited Partnerships [Member]	Dec. 31, 2012 Pension Plan [Member] Interest in Limited Partnerships [Member] Fair Value, Inputs, Level 1 [Member]	Dec. 31, 2011 Pension Plan [Member] Interest in Limited Partnerships [Member] Fair Value, Inputs, Level 1 [Member]	Dec. 31, 2012 Pension Plan [Member] Interest in Limited Partnerships [Member] Fair Value, Inputs, Level 2 [Member]	Dec. 31, 2011 Pension Plan [Member] Interest in Limited Partnerships [Member] Fair Value, Inputs, Level 2 [Member]	Dec. 31, 2012 Pension Plan [Member] Interest in Limited Partnerships [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2011 Pension Plan [Member] Interest in Limited Partnerships [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2012 Pension Plan [Member] Insurance Contracts [Member]	Dec. 31, 2011 Pension Plan [Member] Insurance Contracts [Member]	Dec. 31, 2012 Pension Plan [Member] Insurance Contracts [Member] Fair Value, Inputs, Level 1 [Member]	Dec. 31, 2011 Pension Plan [Member] Insurance Contracts [Member] Fair Value, Inputs, Level 1 [Member]	Dec. 31, 2012 Pension Plan [Member] Insurance Contracts [Member] Fair Value, Inputs, Level 2 [Member]	Dec. 31, 2011 Pension Plan [Member] Insurance Contracts [Member] Fair Value, Inputs, Level 2 [Member]	Dec. 31, 2012 Pension Plan [Member] Insurance Contracts [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2011 Pension Plan [Member] Insurance Contracts [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2012 Pension Plan [Member] Other Investment [Member]	Dec. 31, 2011 Pension Plan [Member] Other Investment [Member]	Dec. 31, 2012 Pension Plan [Member] Other Investment [Member] Fair Value, Inputs, Level 1 [Member]	Dec. 31, 2011 Pension Plan [Member] Other Investment [Member] Fair Value, Inputs, Level 1 [Member]	Dec. 31, 2012 Pension Plan [Member] Other Investment [Member] Fair Value, Inputs, Level 2 [Member]	Dec. 31, 2011 Pension Plan [Member] Other Investment [Member] Fair Value, Inputs, Level 2 [Member]	Dec. 31, 2012 Pension Plan [Member] Other Investment [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2011 Pension Plan [Member] Other Investment [Member] Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2012 Interest in Limited Partnerships [Member]	Dec. 31, 2011 Interest in Limited Partnerships [Member]	Dec. 31, 2012 Commingled Funds [Member]	Dec. 31, 2011 Commingled Funds [Member]	Dec. 31, 2012 Morgan Stanley Institutional Cayman Fund LP [Member]		Dec. 31, 2012 JPM Multi Strat II C A Ser 11 07 [Member]		Dec. 31, 2012 RII World Timberfund, LLC [Member]		Dec. 31, 2012 MS IFHF SVP LP Cayman [Member]		Dec. 31, 2012 MS IFHF SVP LP Alpha [Member]		Dec. 31, 2012 Comm Drive, LLC [Member]		Dec. 31, 2012 CTE Drive, LLC [Member]		Dec. 31, 2012 Oakbrook Parkway LLC [Member]		Dec. 31, 2012 West Jefferson, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of plan assets			$ 5,055	$ 5,101	$ 6,240	$ 1,253,666	$ 1,257,990	$ 1,290,274
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of year	101,678																																																																																										104,033	42,635	37,194	37,378
Realized gains/(losses)																																																																																											5,587	378	0	12
Unrealized gains/(losses)																																																																																											454	317	2,620	(196)
Contributed assets																																																																																												58,100		0
Purchases																																																																																												10,101		37,390
Sales																																																																																											(8,396)	(7,498)	0	(37,390)
Balance, end of year	101,678																																																																																										101,678	104,033	39,814	37,194	33,535	[1]	39,814	[2]	5,569	[3]	4,649	[1]	2,523	[1]	6,782	[4]	5,405	[4]	20,106	[4]	23,109	[4]
Fair Value	101,678																																																																																										101,678	104,033	39,814	37,194	33,535	[1]	39,814	[2]	5,569	[3]	4,649	[1]	2,523	[1]	6,782	[4]	5,405	[4]	20,106	[4]	23,109	[4]
Redemption Frequency																																																																																															Quarterly	[1]	Quarterly	[2]	Through liquidation of underlying investments	[3]	Through liquidation of underlying investments	[1]	Through liquidation of underlying investments	[1]	Through liquidation of underlying investments	[4]	Through liquidation of underlying investments	[4]	Through liquidation of underlying investments	[4]	Through liquidation of underlying investments	[4]
Redemption Notice Period (in days)																																																																																															P60D	[1]	P65D	[2]	0	[3]	0	[1]	0	[1]	0	[4]	0	[4]	0	[4]	0	[4]
Liquidation Period (in years)																																																																																																			10 years	[3]	2 years	[1]	2 years	[1]
Defined Benefit Plan Disclosure [Line Items]
Total investments, at fair value						1,250,653	1,196,140		232,792	335,443	876,369	719,470	141,492	141,227	42,391	34,087	0	0	42,391	34,087	0	0	14,166	120,802	0	0	14,166	120,802	0	0	246,024	323,075	0	0	246,024	323,075	0	0	133,631	251,776	133,631	251,776	0	0	0	0	345,532	99,063	0	0	305,718	61,869	39,814	37,194	8,606	0	8,606	0	366,336	253,752	99,161	83,667	267,175	170,085	0	0	101,678	104,033	0	0	0	0	101,678	104,033	799	805	0	0	799	805	0	0	96	141	0	0	96	141	0	0
Receivable for Plan Assets of Acquired Business							51,634
Receivable for Earnings on Plan Assets of Acquired Business							8,869
Interest and Dividends Receivable						3,252	2,835
Due from Broker for Securities Sold						3,788	30,085
Receivable Associated with Insurance Contract						7,610	7,727
Due to Broker for Securities Purchased						(11,637)	(39,300)
Total Plan Assets, at Fair Value			5,055	5,101	6,240	1,253,666	1,257,990	1,290,274
Long-term debt [Abstract]
Carrying Amount	8,381,947	8,224,392
Fair Value	$ 9,091,416	$ 7,958,873

[1] The partnership investment objective is to seek capital appreciation principally through investing in investment funds managed by third party investment managers who employ a variety of alternative investment strategies.

[2] The fund's investment objective is to generate long-term capital appreciation with relatively low volatility and a low correlation with traditional equity and fixed-income markets. The fund seeks to accomplish this objective by allocating its assets primarily among a select group of experienced portfolio managers that invest in a variety of markets, either through the medium of investment funds or through discretionary managed accounts.

[3] The partnership's objective is to realize substantial long-term capital appreciation by investing in timberland properties primarily in South America, New Zealand and Australia.

[4] The partnership invests in commercial real estate properties that are leased to the Company. The leases are triple net, whereby the Company is responsible for all expenses, including but not limited to, insurance, repairs and maintenance and payment of property taxes.