Pension and Other Post-Retirement Plans (Details 4) (USD $)	3 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2012	Dec. 31, 2011		Dec. 31, 2010
U.K. Plan
Pension and Other Post-Retirement Plans
Decrease in benefit obligation due to plan amendment	$ 5,825
Maximum increase in pensionable earnings	2.00%
Change in fair value of the pension assets valued using significant unobservable inputs (Level 3)
Fair value of plan assets at beginning of year		42,538,000
Fair value of assets at end of year		52,120,000	42,538,000
Expected benefit payments
2013		894,000
2014		910,000
2015		926,000
2016		942,000
2017		959,000
2018-2022		5,085,000
Weighted average actuarial assumptions used to determine the benefit obligation and net periodic benefit cost
Discount rate used to calculate benefit obligation (as a percent)		4.50%	4.80%		5.40%
Discount rate used to calculate net periodic pension cost (as a percent)		4.80%	5.40%		5.80%
Rate of compensation increase (as a percent)		2.00%	3.50%		4.00%
Expected return on assets (as a percent)		6.80%	7.50%		7.80%
Canadian Plan
Change in fair value of the pension assets valued using significant unobservable inputs (Level 3)
Fair value of plan assets at beginning of year		30,658,000
Fair value of assets at end of year		35,921,000	30,658,000
Expected benefit payments
2013		1,507,000
2014		1,537,000
2015		1,637,000
2016		1,707,000
2017		1,853,000
2018-2022		12,210,000
Weighted average actuarial assumptions used to determine the benefit obligation and net periodic benefit cost
Discount rate used to calculate benefit obligation (as a percent)		4.50%	5.30%		5.50%
Discount rate used to calculate net periodic pension cost (as a percent)		5.30%	5.50%		6.40%
Rate of compensation increase (as a percent)		3.25%	3.25%		3.25%
Expected return on assets (as a percent)		6.50%	7.00%		7.00%
Significant Unobservable Inputs (Level 3) | U.K. Plan
Change in fair value of the pension assets valued using significant unobservable inputs (Level 3)
Fair value of plan assets at beginning of year		9,356,000	2,416,000
Purchases		192,000	6,616,000
Unrealized gain on asset still held, at end of year		883,000	324,000
Fair value of assets at end of year			9,356,000
Real estate | U.K. Plan
Change in fair value of the pension assets valued using significant unobservable inputs (Level 3)
Fair value of assets at end of year		10,431,000	9,356,000	[1]
Real estate | Significant Unobservable Inputs (Level 3) | U.K. Plan
Change in fair value of the pension assets valued using significant unobservable inputs (Level 3)
Fair value of assets at end of year		$ 10,431,000	$ 9,356,000	[1]

[1] The assets are invested through managed funds that are valued using inputs derived principally from quoted prices in active markets for the underlying assets in the fund.