Employee Benefit Plans (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
Defined pension plan benefits [Member]
Components of net periodic benefit cost
Service cost - benefits earned during the year	$ 12	$ 143	$ 24	$ 286
Interest cost on projected benefit obligations	571	627	1,128	1,254
Expected return on plan assets	(803)	(945)	(1,595)	(1,889)
Amortization of prior service cost		49		98
Amortization of net (gain) loss	(154)	449	368	898
Net periodic benefit cost	(374)	323	(75)	647
Other postretirement benefits [Member]
Components of net periodic benefit cost
Service cost - benefits earned during the year	39	37	78	74
Interest cost on projected benefit obligations	76	81	152	162
Expected return on plan assets
Amortization of prior service cost	40	40	80	80
Amortization of net (gain) loss
Net periodic benefit cost	$ 155	$ 158	$ 310	$ 316