Balance sheet components - Inventories and Held for Sale (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended
	Dec. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Apr. 30, 2019
Long Lived Assets Held-for-sale [Line Items]
Raw materials	$ 27,806	$ 24,083		$ 24,083		$ 27,806
Work in process	13,044	14,892		14,892		13,044
Finished goods	11,309	9,820		9,820		11,309
Inventories	52,159	48,795		48,795		52,159
Finished goods, at vendor managed inventory locations	5,600	2,800		2,800		5,600
Restructuring charges		79	$ 622	258	$ 653
Assets held for sale	2,971	0		0		2,971
Gain on asset sale		817	$ 0	817	$ 0		$ 2,200
NeoPhotonics Corporation, LLC | Disposed of by Sale
Long Lived Assets Held-for-sale [Line Items]
Percent of ownership disposed								100.00%
Consideration received								$ 2,000
Exit fee settlements								$ 2,000
Gain on asset sale		$ 800		$ 800
Property, plant and equipment
Long Lived Assets Held-for-sale [Line Items]
Assets held for sale	2,500					2,500
Prepaid Expenses and Other Current Assets
Long Lived Assets Held-for-sale [Line Items]
Assets held for sale	500					500
Rusnano Group
Long Lived Assets Held-for-sale [Line Items]
Restructuring charges						1,600
Rusnano Group | Derivative
Long Lived Assets Held-for-sale [Line Items]
Accrued payments	$ 2,000					$ 2,000
NeoPhotonics Corporation | Joint Stock Company Rusnano
Long Lived Assets Held-for-sale [Line Items]
Assets held for sale, percent of component acquired	100.00%