Retirement Plans and Other Postretirement Benefits (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Retirement Plans [Member]
Components of net periodic benefit cost
Service cost	$ 155	$ 184	$ 313	$ 278
Interest cost	432	433	863	863
Expected return on plan assets	(637)	(476)	(1,128)	(948)
Amortization of net loss	287	176	578	364
Accretion of prior service cost	(59)	(58)	(118)	(117)
Net periodic cost	178	259	508	440
Other Post Retirement Benefits [Member]
Components of net periodic benefit cost
Service cost	20	17	41	33
Interest cost	29	30	59	59
Expected return on plan assets
Amortization of net loss	5		11	17
Accretion of prior service cost	(5)	(5)	(10)	(10)
Net periodic cost	$ 49	$ 42	$ 101	$ 99