Income taxes - Components of Deferred Income Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred Tax Assets:
Net operating loss carryforwards	$ 54,339	$ 56,828
Federal and state credits	30,111	28,328
Reserves, accruals and other	14,132	11,265
Fixed assets and intangibles	2,783	2,398
Total deferred tax assets	101,365	98,819
Valuation allowance	(92,149)	(92,891)
Total deferred tax assets, net of valuation allowance	9,216	5,928
Less deferred tax liabilities:
Acquired intangibles	(283)	(313)
Property, plant and equipment	(4,663)	(4,754)
Right-of-Use Lease Assets	(3,124)	0
Net deferred tax assets	1,146	861
Reported as:
Long term deferred tax assets, included within other long-term assets	1,674	861
Long term deferred income tax liabilities, included within noncurrent liabilities	(528)	0
Net deferred tax assets	$ 1,146	$ 861