Retirement Plans - Reconciliation of changes in projected benefit obligations (Details) (Pension Plans [Member], USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Pension Plans [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Accumulated benefit obligation at beginning of year	$ 6,591	$ 5,973
Service cost	70	74	39
Interest cost	287	303	320
Actuarial loss	600	724
Expenses paid	(31)	(70)
Benefits paid	(408)	(413)
Accumulated benefit obligation at end of year	$ 7,109	$ 6,591	$ 5,973