Employee Benefit Plans (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Pension Benefits [Member]
Components of the net periodic benefit cost
Service cost
Interest cost	1,143	1,126
Expected return on plan assets	(1,539)	(1,560)
Recognized net actuarial loss	450	223
Benefit cost (income)	54	(211)
Postretirement Benefits [Member]
Components of the net periodic benefit cost
Service cost	192	141
Interest cost	333	318
Amortization of prior service cost	(136)	(136)
Recognized net actuarial loss	327	209
Benefit cost (income)	$ 716	$ 532