Retirement Plans and Other Postretirement Benefits (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 end of year	$ 34,420	$ 25,213
Retirement Plans [Member]
Change in benefit obligation:
Benefit obligation at beginning of year	38,374	32,250
Service cost	622	556	362
Interest cost	1,726	1,725	1,708
Actuarial loss	3,755	5,368
Benefits paid	(1,598)	(1,525)
Benefit obligation at end of year	42,879	38,374	32,250
Change in plan assets:
Fair value of plan assets at beginning of year	25,213	24,366
Actual return on plan assets	2,669	127
Benefits paid	(1,598)	(1,525)
Employer contribution and non-qualified benefit payments	8,136	2,245
Fair value of plan assets at end of year	34,420	25,213	24,366
Funded status	(8,459)	(13,161)
Unrecognized net actuarial loss	22,576	20,482
Unrecognized prior service costs	(1,825)	(2,061)
Net amount recognized	12,292	5,260
Other Post Retirement Benefits [Member]
Change in benefit obligation:
Benefit obligation at beginning of year	2,344	1,974
Service cost	82	66	76
Interest cost	116	117	115
Actuarial loss	55	267
Benefits paid	(79)	(80)
Benefit obligation at end of year	2,518	2,344	1,974
Change in plan assets:
Fair value of plan assets at beginning of year
Actual return on plan assets
Benefits paid	(79)	(80)
Employer contribution and non-qualified benefit payments	79	80
Fair value of plan assets at end of year
Funded status	(2,518)	(2,344)
Unrecognized net actuarial loss	850	819
Unrecognized prior service costs	(27)	(48)
Net amount recognized	$ (1,695)	$ (1,573)