Income Taxes - Summary of deferred tax assets related to loss carryforwards and tax credits (Details 4) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Deferred Tax Assets Related To Loss Carryforwards And Tax Credits [Line Items]
Total tax effected loss carryforward		$ 68,518	$ 91,832
Total credit carryforward		181,851	164,841
U.S.
Deferred Tax Assets Related To Loss Carryforwards And Tax Credits [Line Items]
Total tax effected loss carryforward	[1]	7,117	27,405
U.S. | R&D
Deferred Tax Assets Related To Loss Carryforwards And Tax Credits [Line Items]
Total credit carryforward		119,257	103,581
U.S. | Other Tax Credit Carryforward
Deferred Tax Assets Related To Loss Carryforwards And Tax Credits [Line Items]
Total credit carryforward		0	5,742
Non-U.S.
Deferred Tax Assets Related To Loss Carryforwards And Tax Credits [Line Items]
Total tax effected loss carryforward		$ 17,846	18,556
Operating loss carryforward expiration description	[2]	Varies
Non-U.S. | Other US States | R&D
Deferred Tax Assets Related To Loss Carryforwards And Tax Credits [Line Items]
Total credit carryforward		$ 22,259
Foreign | Georgia
Deferred Tax Assets Related To Loss Carryforwards And Tax Credits [Line Items]
Total tax effected loss carryforward		15,211	15,948
Foreign | Pennsylvania
Deferred Tax Assets Related To Loss Carryforwards And Tax Credits [Line Items]
Total tax effected loss carryforward		17,400	17,687
Foreign | California | R&D
Deferred Tax Assets Related To Loss Carryforwards And Tax Credits [Line Items]
Total credit carryforward		$ 40,335	34,208
Tax credit carryforwards expiration description		Indefinite
Foreign | Other US States
Deferred Tax Assets Related To Loss Carryforwards And Tax Credits [Line Items]
Total tax effected loss carryforward		$ 10,944	12,236
Foreign | Other US States | R&D
Deferred Tax Assets Related To Loss Carryforwards And Tax Credits [Line Items]
Total credit carryforward			$ 21,310
Minimum | U.S.
Deferred Tax Assets Related To Loss Carryforwards And Tax Credits [Line Items]
Operating loss carryforwards date	[1]	Dec. 31, 2019
Minimum | U.S. | R&D
Deferred Tax Assets Related To Loss Carryforwards And Tax Credits [Line Items]
Tax credit carryforwards date		Dec. 31, 2019
Minimum | Foreign | Georgia
Deferred Tax Assets Related To Loss Carryforwards And Tax Credits [Line Items]
Operating loss carryforwards date		Dec. 31, 2019
Minimum | Foreign | Pennsylvania
Deferred Tax Assets Related To Loss Carryforwards And Tax Credits [Line Items]
Operating loss carryforwards date		Dec. 31, 2019
Minimum | Foreign | Other US States
Deferred Tax Assets Related To Loss Carryforwards And Tax Credits [Line Items]
Operating loss carryforwards date		Dec. 31, 2019
Minimum | Foreign | Other US States | R&D
Deferred Tax Assets Related To Loss Carryforwards And Tax Credits [Line Items]
Tax credit carryforwards date		Dec. 31, 2019
Maximum | U.S.
Deferred Tax Assets Related To Loss Carryforwards And Tax Credits [Line Items]
Operating loss carryforwards date	[1]	Dec. 31, 2029
Maximum | U.S. | R&D
Deferred Tax Assets Related To Loss Carryforwards And Tax Credits [Line Items]
Tax credit carryforwards date		Dec. 31, 2038
Maximum | Foreign | Georgia
Deferred Tax Assets Related To Loss Carryforwards And Tax Credits [Line Items]
Operating loss carryforwards date		Dec. 31, 2038
Maximum | Foreign | Pennsylvania
Deferred Tax Assets Related To Loss Carryforwards And Tax Credits [Line Items]
Operating loss carryforwards date		Dec. 31, 2038
Maximum | Foreign | Other US States
Deferred Tax Assets Related To Loss Carryforwards And Tax Credits [Line Items]
Operating loss carryforwards date		Dec. 31, 2038
Maximum | Foreign | Other US States | R&D
Deferred Tax Assets Related To Loss Carryforwards And Tax Credits [Line Items]
Tax credit carryforwards date		Dec. 31, 2038

[1] Gross of tax effect U.S. Federal operating loss carryforwards are $33.9 million for the year ended December 31, 2018 and $130.5 million for the year ended December 31, 2017.

[2] $2.9 million of this amount is located in Mexico and Israel, both of which have an expiration of ten years, Canadian NOLs expire within 16 years and all other foreign NOLs have an indefinite carryforward life.