Benefit plans (Details) (USD $)	12 Months Ended																								12 Months Ended
	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Dec. 31, 2011 Pension and Supplemental Executive Retirement Plans [Member]		Dec. 31, 2010 Pension and Supplemental Executive Retirement Plans [Member]		Dec. 31, 2009 Pension and Supplemental Executive Retirement Plans [Member]	Dec. 31, 2011 Other Postretirement Benefits [Member]		Dec. 31, 2010 Other Postretirement Benefits [Member]		Dec. 31, 2009 Other Postretirement Benefits [Member]	Dec. 31, 2011 Other Postretirement Benefits [Member] Domestic Mutual Funds [Member]	Dec. 31, 2011 Other Postretirement Benefits [Member] International Mutual Funds [Member]	Dec. 31, 2011 Other Postretirement Benefits [Member] Level 1 [Member]	Dec. 31, 2011 Other Postretirement Benefits [Member] Level 1 [Member] Domestic Mutual Funds [Member]	Dec. 31, 2011 Other Postretirement Benefits [Member] Level 1 [Member] International Mutual Funds [Member]	Dec. 31, 2011 Other Postretirement Benefits [Member] Level 2 [Member]	Dec. 31, 2011 Other Postretirement Benefits [Member] Level 2 [Member] Domestic Mutual Funds [Member]	Dec. 31, 2011 Other Postretirement Benefits [Member] Level 2 [Member] International Mutual Funds [Member]	Dec. 31, 2011 Other Postretirement Benefits [Member] Level 3 [Member]	Dec. 31, 2011 Other Postretirement Benefits [Member] Level 3 [Member] Domestic Mutual Funds [Member]	Dec. 31, 2011 Other Postretirement Benefits [Member] Level 3 [Member] International Mutual Funds [Member]	Dec. 31, 2011 Pension Plan [Member]	Dec. 31, 2010 Pension Plan [Member]	Dec. 31, 2011 Pension Plan [Member] Domestic Mutual Funds [Member]	Dec. 31, 2011 Pension Plan [Member] Common Stocks [Member]	Dec. 31, 2011 Pension Plan [Member] Corporate Bonds [Member]	Dec. 31, 2011 Pension Plan [Member] U.S. Government Securities [Member]	Dec. 31, 2011 Pension Plan [Member] Municipals [Member]	Dec. 31, 2011 Pension Plan [Member] Foreign Bonds [Member]	Dec. 31, 2011 Pension Plan [Member] Foreign Stocks [Member]	Dec. 31, 2011 Pension Plan [Member] International Mutual Funds [Member]	Dec. 31, 2011 Pension Plan [Member] Level 1 [Member]	Dec. 31, 2011 Pension Plan [Member] Level 1 [Member] Domestic Mutual Funds [Member]	Dec. 31, 2011 Pension Plan [Member] Level 1 [Member] Common Stocks [Member]	Dec. 31, 2011 Pension Plan [Member] Level 1 [Member] Corporate Bonds [Member]	Dec. 31, 2011 Pension Plan [Member] Level 1 [Member] U.S. Government Securities [Member]	Dec. 31, 2011 Pension Plan [Member] Level 1 [Member] Municipals [Member]	Dec. 31, 2011 Pension Plan [Member] Level 1 [Member] Foreign Bonds [Member]	Dec. 31, 2011 Pension Plan [Member] Level 1 [Member] Foreign Stocks [Member]	Dec. 31, 2011 Pension Plan [Member] Level 1 [Member] International Mutual Funds [Member]	Dec. 31, 2011 Pension Plan [Member] Level 2 [Member]	Dec. 31, 2011 Pension Plan [Member] Level 2 [Member] Domestic Mutual Funds [Member]	Dec. 31, 2011 Pension Plan [Member] Level 2 [Member] Common Stocks [Member]	Dec. 31, 2011 Pension Plan [Member] Level 2 [Member] Corporate Bonds [Member]	Dec. 31, 2011 Pension Plan [Member] Level 2 [Member] U.S. Government Securities [Member]	Dec. 31, 2011 Pension Plan [Member] Level 2 [Member] Municipals [Member]	Dec. 31, 2011 Pension Plan [Member] Level 2 [Member] Foreign Bonds [Member]	Dec. 31, 2011 Pension Plan [Member] Level 2 [Member] Foreign Stocks [Member]	Dec. 31, 2011 Pension Plan [Member] Level 2 [Member] International Mutual Funds [Member]	Dec. 31, 2011 Pension Plan [Member] Level 3 [Member]	Dec. 31, 2011 Pension Plan [Member] Level 3 [Member] Domestic Mutual Funds [Member]	Dec. 31, 2011 Pension Plan [Member] Level 3 [Member] Common Stocks [Member]	Dec. 31, 2011 Pension Plan [Member] Level 3 [Member] Corporate Bonds [Member]	Dec. 31, 2011 Pension Plan [Member] Level 3 [Member] U.S. Government Securities [Member]	Dec. 31, 2011 Pension Plan [Member] Level 3 [Member] Municipals [Member]	Dec. 31, 2011 Pension Plan [Member] Level 3 [Member] Foreign Bonds [Member]	Dec. 31, 2011 Pension Plan [Member] Level 3 [Member] Foreign Stocks [Member]	Dec. 31, 2011 Pension Plan [Member] Level 3 [Member] International Mutual Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Age of retirees at which retirement benefits under the plan are terminated (in years)											65
Components of Net Periodic Benefit Cost [Abstract]
Company Service Cost				$ 8,917,000		$ 8,531,000		$ 8,154,000	$ 1,090,000		$ 1,126,000		$ 1,280,000
Interest Cost				16,098,000		15,535,000		14,300,000	1,350,000		1,183,000		1,463,000
Expected Return on Assets				(17,373,000)		(14,502,000)		(15,340,000)	(3,299,000)		(2,891,000)		(2,229,000)
Other Adjustments				0		0		0	0		0		0
Subtotal				7,642,000		9,564,000		7,114,000	(859,000)		(582,000)		514,000
Amortization of Net Transition Obligation/(Asset)				0		0		0	0		0		0
Amortization of Net Prior Service Cost/(Credit)				661,000		650,000		716,000	(6,217,000)		(6,138,000)		(6,059,000)
Amortization of Net Losses/(Gains)				4,010,000		5,924,000		6,330,000	632,000		764,000		1,704,000
Total Amortization				4,671,000		6,574,000		7,046,000	(5,585,000)		(5,374,000)		(4,355,000)
Net Periodic Benefit Cost				12,313,000		16,138,000		14,160,000	(6,445,000)		(5,956,000)		(3,841,000)
Cost of settlements or curtailments				0		0		0	0		0		0
Total Expense for Year				12,313,000		16,138,000		14,160,000	(6,445,000)		(5,956,000)		(3,841,000)
Actuarial Value of Benefit Obligations [Abstract]
Measurement Date				12/31/2011		12/31/2010			12/31/2011		12/31/2010
Accumulated Benefit Obligation				297,145,000		270,684,000			25,007,000		26,200,000
Funded Status [Abstract]
Projected Accumulated Benefit Obligation				(318,048,000)		(291,456,000)		(258,592,000)	(25,007,000)		(26,200,000)		(24,144,000)
Plan Assets at Fair Value				305,748,000		284,080,000		243,369,000	42,578,000		44,362,000		38,920,000	30,229,000	12,349,000	42,578,000	30,229,000	12,349,000	0	0	0	0	0	0	305,748,000		58,699,000	45,770,000	118,575,000	13,137,000	18,362,000	15,411,000	3,130,000	32,664,000	153,400,000	58,699,000	45,770,000	0	13,137,000	0	0	3,130,000	32,664,000	152,348,000	0	0	118,575,000	0	18,362,000	15,411,000	0	0	0	0	0	0	0	0	0	0	0
Funded Status - Overfunded/(Underfunded)				(12,300,000)		(7,376,000)			17,571,000		18,162,000
Accumulated Other Comprehensive Income [Abstract]
Net Actuarial (Gain)/Loss				95,298,000		81,802,000			14,109,000		13,463,000
Net Prior Service Cost/(Credit)				2,278,000		2,847,000			(41,072,000)		(47,290,000)
Net Transition Obligation/(Asset)				0		0			0		0
Total at Year End				97,576,000		84,649,000		93,403,000	(26,964,000)		(33,827,000)		(36,190,000)
Change in Projected Benefit Obligation [Roll Forward]
Benefit Obligation at Beginning of Year				291,456,000		258,592,000			26,200,000		24,144,000
Company Service Cost				8,917,000		8,531,000		8,154,000	1,090,000		1,126,000		1,280,000
Interest Cost				16,098,000		15,535,000		14,300,000	1,350,000		1,183,000		1,463,000
Plan Participants' Contributions				0		0			261,000		327,000
Net Actuarial (Gain)/Loss due to Assumption Changes				23,037,000		10,425,000			397,000		(2,925,000)
Net Actuarial (Gain)/Loss due to Plan Experience				(6,544,000)		3,624,000			(3,643,000)		3,695,000
Benefit Payments from Fund				(14,692,000)	[1]	(5,769,000)	[1]		(560,000)	[1]	(510,000)	[1]
Benefit Payments Directly by Company				(316,000)		(231,000)			(87,000)		(120,000)
Plan Amendments				92,000		749,000			0		(720,000)
Other Adjustment				0		0			0		0
Benefit Obligation at End of Year				318,048,000		291,456,000		258,592,000	25,007,000		26,200,000		24,144,000
Lump sum pension plan benefit payments																									8,200,000
Maximum amount of eligible participant vested benefits for which lump sum payment can be elected																									50,000
Change in Plan Assets [Roll Forward]
Fair Value of Plan Assets at Beginning of Year				284,080,000		243,369,000			44,362,000		38,920,000			30,229,000	12,349,000	42,578,000	30,229,000	12,349,000	0	0	0	0	0	0			58,699,000	45,770,000	118,575,000	13,137,000	18,362,000	15,411,000	3,130,000	32,664,000	153,400,000	58,699,000	45,770,000	0	13,137,000	0	0	3,130,000	32,664,000	152,348,000	0	0	118,575,000	0	18,362,000	15,411,000	0	0	0	0	0	0	0	0	0	0	0
Company Contributions				20,316,000		15,231,000			0		0
Plan Participants' Contributions				0		0			261,000		327,000
Benefit Payments from Fund				(14,692,000)	[1]	(5,769,000)	[1]		(560,000)	[1]	(510,000)	[1]
Benefit Payments paid directly by Company				(316,000)		(231,000)			(87,000)		(120,000)
Actual Return on Assets				16,360,000		31,480,000			(1,224,000)		5,951,000
Other Adjustment				0		0			(173,000)		(207,000)
Fair Value of Plan Assets at End of Year				305,748,000		284,080,000		243,369,000	42,578,000		44,362,000		38,920,000	30,229,000	12,349,000	42,578,000	30,229,000	12,349,000	0	0	0	0	0	0	305,748,000		58,699,000	45,770,000	118,575,000	13,137,000	18,362,000	15,411,000	3,130,000	32,664,000	153,400,000	58,699,000	45,770,000	0	13,137,000	0	0	3,130,000	32,664,000	152,348,000	0	0	118,575,000	0	18,362,000	15,411,000	0	0	0	0	0	0	0	0	0	0	0
Change in Accumulated Other Comprehensive Income (AOCI) [Abstract]
AOCI in Prior Year				84,649,000		93,403,000			(33,827,000)		(36,190,000)
Increase/(Decrease) in AOCI [Abstract]
Recognized during year - Prior Service (Cost)/Credit				(661,000)		(650,000)			6,217,000		6,138,000
Recognized during year - Net Actuarial (Losses)/Gains				(4,010,000)		(5,924,000)			(632,000)		(764,000)
Occurring during year - Prior Service Cost/(Credit)				92,000		749,000			0		(720,000)
Occurring during year - Net Actuarial Losses/(Gains)				17,507,000		(2,929,000)			1,278,000		(2,291,000)
AOCI in Current Year				97,576,000		84,649,000		93,403,000	(26,964,000)		(33,827,000)		(36,190,000)
Amortizations Expected to be Recognized During Next Fiscal Year [Abstract]
Amortization of Net Transition Obligation/(Asset)				0					0
Amortization of Prior Service Cost/(Credit)				643,000					(6,217,000)
Amortization of Net Losses/(Gains)				5,911,000					842,000
Weighted-Average Assumptions Used to Determine Benefit Obligations [Abstract]
Discount Rate (in hundredths)				5.25%		5.75%			4.75%		5.50%
Rate of Compensation Increase (in hundredths)				3.00%		3.00%
Weighted-Average Assumptions Used to Determine Net Periodic Benefit Cost [Abstract]
Discount Rate (in hundredths)				5.75%		6.00%			5.50%		5.75%
Expected Long-term Return on Plan Assets (in hundredths)				6.00%		6.00%			7.50%		7.50%
Rate of Compensation Increase (in hundredths)				3.00%		3.00%
Assumed Health Care Cost Trend Rates at year end [Abstract]
Health Care Cost Trend Rate Assumed for Next Year (in hundredths)									8.00%		8.50%
Rate to Which the Cost Trend Rate is Assumed to Decline (Ultimate Trend Rate) (in hundredths)									5.00%		5.00%
Year That the Rate Reaches the Ultimate Trend Rate									2018		2018
Health care trend rate used for pre-65 benefits (in hundredths)											8.00%
Information used in actuarial assumptions [Abstract]
Minimum value of outstanding noncallable bonds used in hypothetical cash flow bond matching exercise	50,000,000
Future earnings period used in determining the expected average rate of earnings (in years)	20Y
Allocation of assets at year end [Abstract]
Equity Securities									100.00%		100.00%														38.00%	38.00%
Debt Securities									0.00%		0.00%														62.00%	62.00%
Other									0.00%		0.00%														0.00%	0.00%
Total									100.00%		100.00%														100.00%	100.00%
Assets at Fair Value [Abstract]
Fair value of plan assets				305,748,000		284,080,000		243,369,000	42,578,000		44,362,000		38,920,000	30,229,000	12,349,000	42,578,000	30,229,000	12,349,000	0	0	0	0	0	0	305,748,000		58,699,000	45,770,000	118,575,000	13,137,000	18,362,000	15,411,000	3,130,000	32,664,000	153,400,000	58,699,000	45,770,000	0	13,137,000	0	0	3,130,000	32,664,000	152,348,000	0	0	118,575,000	0	18,362,000	15,411,000	0	0	0	0	0	0	0	0	0	0	0
Target Allocation of Assets [Abstract]
Minimum period for which plan portfolio returns are expected to achieve stated objectives (in years)											5Y															5Y
Fixed income, minimum (in hundredths)									0.00%																40.00%
Fixed income, maximum (in hundredths)									10.00%																100.00%
Equity, minimum (in hundredths)									90.00%																0.00%
Equity, maximum (in hundredths)									100.00%																60.00%
Cash equivalents, minimum (in hundredths)																									0.00%
Cash equivalents, maximum (in hundredths)																									10.00%
Maximum investment in international oriented funds (in hundredths)											30.00%
Number of international mutual funds									2
Percent of international oriented funds equity allocation in emerging markets (in hundredths)									5.00%
Percent of international oriented funds equity allocation in companies based outside of the United States, primarily Europe and the Pacific Basin (in hundredths)									25.00%
Actual and Estimated Company Contributions [Abstract]
Current				20,316,000		15,231,000			0		0
Current + 1				984,000					0
Actual Benefit Payments [Abstract]
Current				15,008,000					387,000
Expected Benefit Payments [Abstract]
Current + 1				10,377,000					907,000
Current + 2				11,383,000					1,033,000
Current + 3				14,051,000					1,227,000
Current + 4				14,194,000					1,318,000
Current + 5				15,098,000					1,472,000
Current + 6 - 10				95,553,000					10,686,000
Effect of 1% change in the health care trend rate assumption [Abstract]
Effect of 1-percentage point increase on total service and interest cost component									573,000
Effect of 1-percentage point increase on postretirement benefit obligation									4,463,000
Effect of 1-percentage point decrease on total service and interest cost components									(408,000)
Effect of 1-percentage point decrease on postretirement benefit obligation									(3,490,000)
Profit sharing and 401(k) savings plan [Abstract]
Discretionary profit sharing contribution as a percentage of participant's eligible compensation (in hundredths)	5.00%
Matching contribution rate on employees' before-tax contributions, first contribution level (in hundredths)	80.00%
Employee contributions subject to employer match, first contribution level	1,000
Matching contribution rate on employees' before-tax contributions, second contribution level (in hundredths)	40.00%
Employee contributions subject to employer match, second contribution level	2,000
Profit sharing and 401(k) savings plan expenses	$ 3,600,000	$ 3,700,000	$ 3,100,000

[1] In 2011, includes lump sum payments of $8.2 million from our pension plan to eligible participants, which were former employees with vested benefits of $50 thousand or less. Additional former employees may elect this option in 2012.