Retirement Benefits (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 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	$ 2,900,000	$ 1,200,000	$ 8,600,000	$ 3,400,000
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	2,293,000	1,723,000	7,881,000	5,168,000
Interest cost	2,906,000	2,959,000	9,193,000	8,878,000
Expected return on plan assets	(3,243,000)	(3,400,000)	(9,727,000)	(10,199,000)
Amortization of prior service cost	232,000	236,000	697,000	709,000
Amortization of unrecognized net loss (gain)	2,203,000	979,000	7,508,000	2,936,000
Amortization of unrecognized transition asset			0	0
Net periodic benefit cost	4,391,000	2,497,000	15,552,000	7,492,000
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			15,900,000
Estimated future employer contributions for the current fiscal year	100,000		100,000
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	57,000	32,000	170,000	96,000
Interest cost	74,000	87,000	223,000	260,000
Expected return on plan assets	0	0	0	0
Amortization of prior service cost	13,000	13,000	38,000	38,000
Amortization of unrecognized net loss (gain)	(45,000)	(56,000)	(134,000)	(167,000)
Amortization of unrecognized transition asset			0	0
Net periodic benefit cost	99,000	76,000	297,000	227,000
Estimated future employer contributions for the next fiscal year	500,000		500,000
Employer contributions made during the period			500,000
Estimated future employer contributions for the current fiscal year	$ 200,000		$ 200,000