Commitments and Contingencies - Additional Information (Details)	3 Months Ended		9 Months Ended		76 Months Ended
	Sep. 30, 2018 USD ($) ft² employee	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) ft² employee	Sep. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jan. 31, 2019 ft²	Dec. 31, 2017 USD ($)	Feb. 28, 2017 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2012 USD ($) employee
Operating Leased Assets [Line Items]
Operating leases, rent expense	$ 1,700,000	$ 1,400,000	$ 4,600,000	$ 4,300,000
Sale leaseback rent expense	0	0	$ 0	0
Standard warranty period			1 year
Grants receivable										$ 16,500,000
Number of employees to be hired per incentive grant agreement | employee										900
Minimum cumulative employee compensation, recapture period one										$ 108,000,000
Minimum cumulative employee compensation, recapture period three										324,000,000
Cumulative compensation expense incurred	86,000,000		$ 86,000,000
Proceeds from government grants					$ 12,000,000
Grant agreement, maximum possible repayment amount, recapture period two										5,000,000
Grant agreement, maximum possible repayment amount, recapture period three										$ 2,500,000
Grant agreement, recapture provision repayments	1,500,000		1,500,000				$ 1,500,000
Delaware grant obligation	$ 10,469,000		$ 10,469,000				10,469,000
Self-Generation Incentive Program, percentage of incentive issued in the first year			50.00%
Self-Generation Incentive Program, subsequent payment period			5 years
Sunnyvale, California
Operating Leased Assets [Line Items]
Area of real estate property | ft²	31,000		31,000
Delaware
Operating Leased Assets [Line Items]
Number of full time employees | employee	335		335
Subsequent Event | San Jose, California
Operating Leased Assets [Line Items]
Area of real estate property | ft²						181,000
PPA Company V
Operating Leased Assets [Line Items]
PPA expenses	$ 0	$ 0	$ 900,000	$ 3,700,000
Term loan | PPA Company V | Term Loan due December 2021, Non-Recourse
Operating Leased Assets [Line Items]
Debt face amount									$ 131,200,000
Letters of Credit | PPA Company V
Operating Leased Assets [Line Items]
Maximum borrowing capacity								$ 6,200,000	$ 6,400,000
Amount outstanding	$ 4,700,000		$ 4,700,000				$ 4,400,000