Employee Benefit Plans (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Qualified Pension [Member]
Schedule of net periodic benefit cost related to pension and post-retirement healthcare
Service cost	$ 4,638	$ 4,096
Interest cost	3,697	3,662
Expected return on plan assets	(3,170)	(3,279)
Amortization of actuarial loss	1,156	517
Plan settlement	0	356
Net periodic benefit cost	6,321	5,352
Post-retirement Healthcare [Member]
Schedule of net periodic benefit cost related to pension and post-retirement healthcare
Service cost	7,482	6,784
Interest cost	6,493	6,182
Expected return on plan assets	0	(8)
Amortization of actuarial loss	2,235	1,682
Plan settlement	0	0
Net periodic benefit cost	$ 16,210	$ 14,640