Employee Benefit Plans (Details 6) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Pension Benefits
Components of the net periodic benefit cost
Service cost	$ 0	$ 0	$ 0
Interest cost	4,227	4,496	4,578
Expected return on plan assets	(7,005)	(6,145)	(6,236)
Recognized net actuarial loss	1,530	1,497	940
Benefit cost (income)	(1,248)	(152)	(718)
Postretirement Benefits
Components of the net periodic benefit cost
Service cost	841	752	555
Interest cost	1,366	1,319	1,285
Expected return on plan assets	(543)	(543)	(543)
Recognized net actuarial loss	1,473	1,280	901
Benefit cost (income)	$ 3,137	$ 2,808	$ 2,198