Pensions (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Defined Benefit Plan Disclosure [Line Items]
Contributions by employer			$ 1,593
Estimated employer contributions	1,593		1,593
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	297	262	594	525
Interest cost	320	322	640	644
Expected return on plan assets	(411)	(361)	(822)	(721)
Amortization of actuarial loss	175	160	349	320
Amortization of prior service cost	2	5	5	9
Rate-regulated adjustment	15	10	30	19
Net periodic pension expense	$ 398	$ 398	$ 796	$ 796