Employee Benefit Plans (Details 6) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Pension Benefits
Components of the net periodic benefit cost
Service cost	$ 0	$ 0	$ 1,614
Interest cost	4,496	4,578	4,339
Expected return on plan assets	(6,145)	(6,236)	(5,451)
Recognized net actuarial loss	1,497	940	1,817
Benefit cost (income)	(152)	(718)	2,319
Postretirement Benefits
Components of the net periodic benefit cost
Service cost	752	555	465
Interest cost	1,319	1,285	1,213
Expected return on plan assets	(543)	(543)	(511)
Recognized net actuarial loss	1,280	901	691
Benefit cost (income)	$ 2,808	$ 2,198	$ 1,858