Benefit Plans - Funded Status (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Change in plan assets
Fair value of plan assets, end of year	$ 177,973,000	$ 174,358,000
Pension Plans
Change in benefit obligation
Benefit obligation, beginning of year	249,234,000	257,245,000
Interest cost	10,693,000	12,707,000
Actuarial loss (gain)	27,928,000	11,269,000
Benefits paid	(13,500,000)	(7,769,000)
Plan settlements	(18,478,000)	(24,218,000)
Benefit obligation, end of year	255,877,000	249,234,000
Change in plan assets
Fair value of plan assets, beginning of year	174,358,000	187,327,000
Return on plan assets	20,342,000	1,689,000
Employer contributions	15,251,000	17,329,000
Benefits paid	(13,500,000)	(7,769,000)
Plan settlements	(18,478,000)	(24,218,000)
Fair value of plan assets, end of year	177,973,000	174,358,000
Funded status at end of year	(77,904,000)	(74,876,000)
Postretirement Plans
Change in benefit obligation
Benefit obligation, beginning of year	0	1,040,000
Interest cost	0	26,000
Actuarial loss (gain)	0	(727,000)
Benefits paid	0	(339,000)
Plan settlements	0	0
Benefit obligation, end of year	0	0
Change in plan assets
Fair value of plan assets, beginning of year	0	0
Return on plan assets	0	0
Employer contributions	0	339,000
Benefits paid	0	(339,000)
Plan settlements	0	0
Fair value of plan assets, end of year	0	0
Funded status at end of year	$ 0	$ 0