Retirement Benefits (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Retirement Benefits [Abstract]
Number of unfunded non-qualified deferred compensation pension plans	2
Years of service credited under Supplemental Executive Retirement Plan	6 months
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. hourly 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%
Company's expense recorded for these plans	$ 3,200,000	$ 3,300,000
Pension Benefits [Member]
Net periodic benefit cost [Abstract]
Service cost	2,834,000	2,151,000
Interest cost	3,023,000	2,905,000
Expected return on plan assets	(3,547,000)	(3,230,000)
Amortization of prior service cost	221,000	232,000
Amortization of unrecognized net loss (gain)	2,453,000	2,203,000
Net periodic benefit cost	4,984,000	4,261,000
Estimated future employer contributions for the next fiscal year			400,000
Employer Contribution	0
Additional contributions	400,000
Other Benefits [Member]
Net periodic benefit cost [Abstract]
Service cost	11,000	57,000
Interest cost	45,000	74,000
Expected return on plan assets	0	0
Amortization of prior service cost	(63,000)	13,000
Amortization of unrecognized net loss (gain)	(25,000)	(45,000)
Net periodic benefit cost	(32,000)	99,000
Estimated future employer contributions for the next fiscal year			200,000
Employer Contribution	100,000
Additional contributions	$ 100,000