Pension and Other Post-Retirement Plans (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Components of net periodic pension benefit cost
Service cost	$ 639,000	$ 568,000	$ 1,278,000	$ 1,136,000
Interest cost	1,186,000	1,147,000	2,372,000	2,294,000
Expected return on plan assets	(1,409,000)	(1,227,000)	(2,818,000)	(2,454,000)
Amortization of actuarial gains	261,000	251,000	522,000	502,000
Amortization of prior service costs	(65,000)	(19,000)	(130,000)	(38,000)
Net periodic cost	612,000	720,000	1,224,000	1,440,000
Employer's matching contribution on the dollar for the first 6 percent of participant contributions, effective January 1, 2010			$ 37.5
Maximum percentage of participant contributions eligible for Employer contribution match, towards defined contribution plan (as a percent)			6.00%
Percentage of employer's contribution under 401(k) plan matching up to 6 percent of participant contributions subject to maximum percentage of eligible compensation, effective from January 1, 2010 (as a percent)			2.25%
U.K.-based union employees, U.K. Plan
Defined benefit plan disclosure
Number of years of employee's average compensation preceding retirement (in years)			2