Pension Plans - Components of net periodic pension benefit (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Components of net periodic pension cost
Interest cost	$ 217,000	$ 239,000	$ 434,000	$ 479,000
Expected return on plan assets	(285,000)	(291,000)	(570,000)	(581,000)
Recognized net actuarial loss	34,000	38,000	68,000	75,000
Total net periodic pension cost	(34,000)	(14,000)	(68,000)	(27,000)
Employer contribution	$ 50,000	$ 70,000	90,000	$ 70,000
Expected contributions in current fiscal year			$ 120,000