Employee Post-Retirement Benefits (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Components of net periodic benefit cost
Service cost	$ 67	$ 150
Interest cost	120	188
Expected return on plan assets	0	0
Amortization of transition obligation	0	15
Amortization of prior service credits	(236)	(19)
Recognized actuarial loss	120	135
Net periodic benefit cost	$ 71	$ 469