Postretirement Benefit Plans (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
UNITED STATES [Member]
Components of Net Periodic Benefit Cost
Interest cost	$ 1,735	$ 1,761	$ 3,471	$ 3,523
Expected return on plan assets	(2,103)	(2,013)	(4,205)	(4,025)
Amortization of net loss	932	786	1,863	1,571
Net periodic benefit cost	564	534	1,129	1,069
UNITED KINGDOM [Member]
Components of Net Periodic Benefit Cost
Interest cost	210	279	419	555
Expected return on plan assets	(221)	(264)	(441)	(525)
Amortization of net loss	11	52	22	103
Net periodic benefit cost		$ 67		$ 133