Postretirement Benefit Plans (Details 4) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
UNITED STATES [Member]
Components of Net Periodic Benefit Cost
Interest cost	$ 6,880	$ 6,927	$ 7,030
Expected return on plan assets	(8,423)	(8,063)	(7,860)
Amortization of net loss	3,573	2,853	2,068
Net periodic benefit cost	2,030	1,717	1,238
UNITED KINGDOM [Member]
Components of Net Periodic Benefit Cost
Interest cost	841	1,099	1,037
Expected return on plan assets	(888)	(1,042)	(866)
Amortization of net loss	49	204	276
Net periodic benefit cost	$ 2	$ 261	$ 447