Income Taxes - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Examination [Line Items]
Provision for income taxes	$ 5,300	$ 11,646	$ 1,687	$ 82,548
Effective income tax rate		(3.80%)	(0.90%)	(42.40%)
Valuation allowance	244,581	$ 244,581	$ 181,122
Deferred Tax Assets, Operating Loss Carryforwards, Domestic	316,200	316,200
Unrecognized tax benefits	67,025	67,025	41,198	$ 29,938	$ 35,584
Unrecognized that would affect the effective tax rate if recognized	31,900	31,900
Unrecognized tax benefits, interest on income taxes expense		5,200	$ 3,100
Domestic Tax Authority [Member]
Income Tax Examination [Line Items]
Valuation allowance	191,700	191,700
Deferred tax assets, research credit carryforwards	22,600	22,600
Foreign Tax Authority [Member]
Income Tax Examination [Line Items]
Valuation allowance	52,900	52,900
California [Member]
Income Tax Examination [Line Items]
State net operating loss carryforwards	57,300	57,300
California [Member] | State and Local Jurisdiction [Member]
Income Tax Examination [Line Items]
Deferred tax assets, research credit carryforwards	45,000	45,000
Deferred Tax Assets, Tax Credit Carryforwards, General Business	300	300
Other States [Member]
Income Tax Examination [Line Items]
State net operating loss carryforwards	52,100	52,100
Massachusetts [Member] | State and Local Jurisdiction [Member]
Income Tax Examination [Line Items]
Deferred tax assets, research credit carryforwards	2,900	2,900
United Kingdom [Member]
Income Tax Examination [Line Items]
Foreign net operating loss carryforwards	$ 10,500	$ 10,500