Income taxes (Details) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2016	Dec. 31, 2015
Income Tax Contingency [Line Items]
Effective tax rate	31.50%	3.20%
Effective income tax rate increase (decrease), amount	$ 900
Effective income tax rate increase (decrease), percent	28.30%
Decrease in valuation allowance				$ 15,400
Forecast
Income Tax Contingency [Line Items]
Effective tax rate			41.00%