Pension Plan (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Components of net periodic pension cost
Service cost - benefits earned during year	$ 958	$ 681
Interest cost on projected benefit obligation	1,096	965
Expected return on plan assets	(1,603)	(1,378)
Amortization of prior service cost	12	11
Amortization of net loss	822	569
Net periodic pension cost	$ 1,285	$ 848