Retirement plans (Details) - Pension Plans, Defined Benefit [Member] - USD ($)		12 Months Ended
	Dec. 19, 2012	Dec. 31, 2016	Dec. 31, 2015	Sep. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Employer match of eligible compensation of employees		10.00%
Total obligation		$ 770,000	$ 914,000	$ 1,224,000
Total obligation, payable in 2016		200,000		$ 200,000
Annual liability payable to individual retired employees		$ 50,000
Liability recorded at date of acquisition	$ 885,000
Present value discount factor		14.00%
Amount to be amortized, as interest expense	$ 1,027,000
Interest expense		$ 78,000	148,000
Discounts		454,000	$ 606,000
Income from elimination of retirement liability		$ 23,000