Employee Benefit Plans (Details) (USD $) In Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Pension Benefits [Member]
Components of net periodic pension and other post-retirement benefit cost
Service cost	$ 512	$ 451	$ 1,535	$ 1,353
Interest cost	1,794	1,770	5,382	5,310
Expected return on plan assets	(1,947)	(1,869)	(5,843)	(5,607)
Amortization of prior service cost	100	131	301	393
Amortization of actuarial loss	1,004	702	3,013	2,104
Net periodic benefit cost	1,463	1,185	4,388	3,553
Other Post-Retirement Benefits [Member]
Components of net periodic pension and other post-retirement benefit cost
Service cost	187	178	560	534
Interest cost	590	550	1,771	1,650
Expected return on plan assets
Amortization of prior service cost	303	303	910	910
Amortization of actuarial loss
Net periodic benefit cost	$ 1,080	$ 1,031	$ 3,241	$ 3,094