Debt and lease obligations (lease obligations) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Capital lease obligations [Line Items]
Capital lease obligations	$ 2,109	$ 2,379
Capital lease obligations, expiration date	Oct. 31, 2019
Capital lease obligations, future payments
2016	$ 1,078
2017	731
2018	303
2019	47
Total minimum lease payments	2,159
Less portion representing interest	(50)
Present value of minimum lease payments	2,109
Operating lease obligations, future payments
2016	6,626
2017	5,318
2018	3,642
2019	2,979
2020	1,216
Thereafter	2,389
Total minimum lease payments	22,170
Net rental expense	15,372	13,099	$ 11,855
Machinery and equipment [Member]
Capital lease obligations [Line Items]
Machinery and equipment	4,193	2,911
Accumulated depreciation	(1,942)	(926)
Net assets under capital leases	$ 2,251	$ 1,985