Retirement 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
Net periodic defined benefit pension expense
Service cost	$ 667	$ 545	$ 1,333	$ 1,090
Interest cost	554	563	1,109	1,125
Expected return on plan assets	(591)	(560)	(1,181)	(1,120)
Amortization of prior service cost	654	244	814	488
Net periodic benefit expense	$ 1,284	$ 792	$ 2,075	$ 1,583