Retirement Plans - Reconciliation of changes in projected benefit obligations (Details) (Pension Plans [Member], USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pension Plans [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Accumulated benefit obligation at beginning of year	$ 6,150	$ 7,109
Interest cost	280	259	287
Actuarial (gain) loss	1,235	(738)
Expenses paid	(95)	(74)
Benefits paid	(403)	(406)
Accumulated benefit obligation at end of year	$ 7,167	$ 6,150	$ 7,109