Retirement Benefits (Details) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Retirement Benefits [Abstract]
Number Of Unfunded Non Qualified Deferred Compensation Pension Plans	2
Years of service credited under Supplemental Executive Retirement Plan (in years)	0.5Y
Defined benefit postretirement plans [Abstract]
Number of defined benefit postretirement plans	2
Number of defined postretirement plans providing medical benefits	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
Defined contribution retirement plans [Abstract]
Employer contribution match rate, U.S. employees (in hundredths)	75.00%
Maximum employee contribution rate matched by employer, U.S. employees (in hundredths)	6.00%
Maximum employee contribution rate over and above employee contribution rate matched by employer, U.S. employees (in hundredths)	18.00%
Incremental rate by which employee contribution rate may be increased or decreased, U.S. employees (in hundredths)	1.00%
Minimum employer contribution rate, Canadian employees (in hundredths)	3.00%
Maximum employer contribution rate, Canadian employees (in hundredths)	8.00%
Expense recorded	$ 3,300,000	$ 1,200,000
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	2,151,000	1,672,000
Interest cost	2,905,000	3,012,000
Expected return on plan assets	(3,230,000)	(3,404,000)
Amortization of prior service cost	232,000	236,000
Amortization of unrecognized net loss (gain)	2,203,000	909,000
Net periodic benefit cost	4,261,000	2,425,000
Estimated future employer contributions for the next fiscal year, lower range	16,000,000
Estimated future employer contributions for the next fiscal year, upper range	20,000,000
Employer contributions made during the period	100,000
Estimated future employer contributions for the current fiscal year, lower range	15,900,000
Estimated future employer contributions for the current fiscal year, upper range	19,900,000
Other Postretirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	57,000	48,000
Interest cost	74,000	77,000
Expected return on plan assets	0	0
Amortization of prior service cost	13,000	13,000
Amortization of unrecognized net loss (gain)	(45,000)	(61,000)
Net periodic benefit cost	99,000	77,000
Estimated future employer contributions for the next fiscal year	500,000
Employer contributions made during the period	100,000
Estimated future employer contributions for the current fiscal year	$ 400,000