Employee Benefits (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Pension Plan [Member]
Net periodic benefit cost
Service cost	$ 1,282	$ 791
Interest cost	1,262	1,190
Expected return on plan assets	(1,336)	(1,322)
Amortization of prior service cost	0	3
Amortization of net loss	1,106	592
Net periodic benefit cost	2,314	1,254
Estimated 2013 pension plan contribution, disclosed in prior year 10K			7,000
Contribution by employer	1,750
Postretirement Benefit Plan [Member]
Net periodic benefit cost
Service cost	753	496
Interest cost	424	398
Expected return on plan assets	0	0
Amortization of prior service cost	0	(8)
Amortization of net loss	136	56
Net periodic benefit cost	$ 1,313	$ 942