Summary of significant accounting policies - Narrative (Details)	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jan. 01, 2019 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Restricted cash	$ 10,972,000	$ 11,053,000
Goodwill impairment charges	0	0	$ 0
Asset impairment charges	0	1,000,000.0	400,000
Loss on foreign currency contracts		2,200,000
Net gains (losses) resulting from foreign exchange transactions	$ 200,000	$ 1,400,000	$ (500,000)
Conversion of stock, shares issued ratio	1
Operating lease right-of-use assets	$ 15,603,000			$ 17,300,000
Operating lease, liability	$ 18,629,000			$ 20,800,000
Land use rights
Summary Of Significant Accounting Policies [Line Items]
Useful Life	45 years
Minimum
Summary Of Significant Accounting Policies [Line Items]
Useful Life	2 years
Product warranty period	1 year
Maximum
Summary Of Significant Accounting Policies [Line Items]
Useful Life	7 years
Product warranty period	3 years
Notes Receivable
Summary Of Significant Accounting Policies [Line Items]
Receivable due period, general	9 months
Customer Concentration Risk | Customer One | Accounts Receivable
Summary Of Significant Accounting Policies [Line Items]
Percentage of concentration of credit risk	37.00%	35.00%
Customer Concentration Risk | Customer Two | Accounts Receivable
Summary Of Significant Accounting Policies [Line Items]
Percentage of concentration of credit risk	19.00%	17.00%