Employee Benefit Plans (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Change in plan assets
Fair value of plan assets at beginning of year	$ 87,605
Company contributions	3,000
Fair value of plan assets at end of year	99,857
Pension Benefits
Change in benefit obligation
Benefit obligation at beginning of year	109,976	90,603
Service cost	0	0	1,614
Interest cost	4,496	4,578	4,339
Actuarial losses	5,560	16,363
Participant contributions	0	0
Retiree drug subsidy received	0	0
Benefits paid	(2,142)	(1,568)
Benefit obligation at end of year	117,890	109,976	90,603
Change in plan assets
Fair value of plan assets at beginning of year	87,605	84,097
Actual gains (loss) on plan assets	11,178	(91)
Company contributions	3,216	5,167
Participant contributions	0	0
Benefits paid	(2,142)	(1,568)
Fair value of plan assets at end of year	99,857	87,605	84,097
Funded status of plans at end of year	(18,033)	(22,371)
Postretirement Benefits
Change in benefit obligation
Benefit obligation at beginning of year	31,558	24,593
Service cost	752	555	465
Interest cost	1,319	1,285	1,213
Actuarial losses	2,969	6,020
Participant contributions	487	478
Retiree drug subsidy received	168	202
Benefits paid	(1,199)	(1,575)
Benefit obligation at end of year	36,054	31,558	24,593
Change in plan assets
Fair value of plan assets at beginning of year	0	0
Actual gains (loss) on plan assets	0	0
Company contributions	712	1,097
Participant contributions	487	478
Benefits paid	(1,199)	(1,575)
Fair value of plan assets at end of year	0	0	0
Funded status of plans at end of year	$ (36,054)	$ (31,558)