Pension Plan (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
Components of Net Periodic Pension Cost
Service cost benefits earned during year	$ 680	$ 643	$ 1,361	$ 1,279
Interest cost on projected benefit obligation	966	907	1,931	1,803
Expected return on plan assets	(1,378)	(1,412)	(2,756)	(2,808)
Amortization of prior service cost	12	15	23	29
Amortization of net loss	568	318	1,137	633
Net periodic pension cost	$ 848	$ 471	$ 1,696	$ 936