Income taxes - Deferred Tax Liabilities (Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred Tax Liabilities, Gross [Abstract]
Capitalized software	$ 12,202	$ 16,756
Depreciation and amortization	11,756	12,964
Intangible assets	13,490	13,492
Right of use asset	9,833
Unrealized gain on derivative instruments	1,176	1,871
Undistributed earnings of foreign subsidiaries	3,482	3,449
Gross deferred tax liabilities	51,939	48,532
Deferred Tax Assets, Gross [Abstract]
Operating loss carryforwards	(87,074)	(83,013)
Vacation and other accruals	(4,979)	(5,391)
Inventory valuation and warranty provisions	(2,317)	(2,576)
Doubtful accounts and sales provisions	(860)	(890)
Unrealized exchange loss	(1,052)	(1,735)
Deferred revenue	(7,708)	(8,199)
Operating lease liabilities	(10,426)
Accrued expenses	(262)	(848)
Global intangible low-taxed income	(3,444)	(4,339)
Stock-based compensation	(5,809)	(5,216)
Research and development tax credit carryforward	0	(258)
Capital loss carryforward	0	(250)
Foreign tax credit carryforward	(674)	(42)
Outside basis difference on asset held for sale	(10,762)	0
Cumulative translation adjustment on undistributed earnings	(985)	(912)
Other	(2,072)	(1,776)
Gross deferred tax assets	(138,424)	(115,445)
Valuation allowance	85,516	79,624
Net deferred tax liability		$ 12,711
Net deferred tax liability	$ (969)