Postretirement Benefit Plans (Details 5) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
UNITED STATES [Member]
Other changes in plan assets and benefit obligations recognized in other comprehensive income
Net actuarial (gain) loss	$ 4,622	$ 10,552	$ 6,684
Amortization of net actuarial loss	(3,573)	(2,853)	(2,068)
Total recognized in other comprehensive income	1,049	7,699	4,616
Total recognized in net periodic benefit cost and other comprehensive income	3,079	9,416	5,854
UNITED KINGDOM [Member]
Other changes in plan assets and benefit obligations recognized in other comprehensive income
Net actuarial (gain) loss	3,111	(1,742)	(799)
Amortization of net actuarial loss	(49)	(204)	(276)
Total recognized in other comprehensive income	3,062	(1,946)	(1,075)
Total recognized in net periodic benefit cost and other comprehensive income	$ 3,064	$ (1,685)	$ (628)