Benefit Plans (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Pension Benefits
Change in benefit obligation:
Benefit obligation at beginning of year	$ 274,874	$ 232,230
Service cost	2,025	4,642	3,727
Interest cost	10,992	12,212	11,602
Actuarial loss	19,535	35,615
Amendments	5,473
Settlements	(14,560)
Curtailments	(28,192)
Benefits paid	(10,039)	(9,825)
Benefit obligation at end of year	260,108	274,874	232,230
Change in plan assets:
Fair value of plan assets at beginning of year	134,495	129,352
Actual return on plan assets	16,593	(2,638)
Employer Contribution	34,194	17,606
Settlements	(14,560)
Benefits paid	(10,039)	(9,825)
Fair value of plan assets at end of year	160,683	134,495	129,352
Funded status at end of year	(99,425)	(140,379)
Other Postretirement Benefits
Change in benefit obligation:
Benefit obligation at beginning of year	32,515	24,892
Service cost	1,061	529	424
Interest cost	1,378	1,360	1,234
Actuarial loss	1,454	6,629
Benefits paid	(932)	(895)
Benefit obligation at end of year	35,476	32,515	24,892
Change in plan assets:
Employer Contribution	932	895
Benefits paid	(932)	(895)
Funded status at end of year	$ (35,476)	$ (32,515)