Retirement Benefits (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Retirement Benefits [Abstract]
Number of unfunded non qualified deferred compensation pension plans	2		2
Years of service credited under supplemental executive retirement plan	6 months		6 months
Defined benefit postretirement plans [Abstract]
Number of defined benefit postretirement plans	2		2
Number of defined postretirement plans providing medical benefits	1		1
Assumed submitted claims medical trend rate used to fix the amount of the Company's obligation (in hundredths)			9.25%
Year in which submitted claims medical trend rate was determined	1997		1997
Defined contribution retirement plans [Abstract]
Employer contribution match rate, U.S. employees (in hundredths)	75.00%		75.00%
Maximum employee contribution rate matched by employer, U.S. employees (in hundredths)	6.00%		6.00%
Percentage of contributions made by employer (in hundredths)			100.00%
Maximum employee contribution rate over and above employee contribution rate matched by employer, U.S. employees (in hundredths)	18.00%		18.00%
Incremental rate by which employee contribution rate may be increased or decreased, U.S. employees (in hundredths)	1.00%		1.00%
Minimum employer contribution rate, Canadian employees (in hundredths)	3.00%		3.00%
Maximum employer contribution rate, Canadian employees (in hundredths)	8.00%		8.00%
Expense recorded	$ 2,400,000	$ 1,100,000	$ 5,600,000	$ 2,200,000
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	3,437,000	1,775,000	5,588,000	3,447,000
Interest cost	3,382,000	2,908,000	6,288,000	5,920,000
Expected return on plan assets	(3,254,000)	(3,397,000)	(6,484,000)	(6,801,000)
Amortization of prior service cost	232,000	236,000	465,000	473,000
Amortization of unrecognized net loss (gain)	3,102,000	1,049,000	5,305,000	1,958,000
Amortization of unrecognized transition asset			0	0
Net periodic benefit cost	6,899,000	2,571,000	11,162,000	4,997,000
Estimated future employer contributions for the next fiscal year, lower range	16,000,000		16,000,000
Estimated future employer contributions for the next fiscal year, upper range	20,000,000		20,000,000
Employer contributions made during the period			2,300,000
Estimated future employer contributions for the current fiscal year, lower range	12,100,000		12,100,000
Estimated future employer contributions for the current fiscal year, upper range	13,100,000		13,100,000
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	57,000	17,000	113,000	64,000
Interest cost	74,000	96,000	149,000	173,000
Expected return on plan assets	0	0	0	0
Amortization of prior service cost	13,000	13,000	26,000	25,000
Amortization of unrecognized net loss (gain)	(45,000)	(50,000)	(89,000)	(111,000)
Amortization of unrecognized transition asset			0	0
Net periodic benefit cost	99,000	76,000	199,000	151,000
Estimated future employer contributions for the next fiscal year	500,000		500,000
Employer contributions made during the period			300,000
Estimated future employer contributions for the current fiscal year	$ 400,000		$ 400,000