Retirement Plans - Net periodic pension cost (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 Disclosure [Line Items]
Service cost	$ 70	$ 74	$ 39
Interest cost	287	303	320
Expected return on assets	(306)	(309)	(300)
Amortization of net loss	101	64	59
Net periodic pension cost	$ 152	$ 132	$ 118