Commitments and Contingencies - Additional Information (Details)	3 Months Ended		6 Months Ended		76 Months Ended
	Jun. 30, 2018 USD ($) ft² employee	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) ft² employee	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) ft² employee	Jan. 31, 2019 ft²	Dec. 31, 2017 USD ($)	Mar. 31, 2012 USD ($) employee
Operating Leased Assets [Line Items]
Operating leases, rent expense	$ 1,400,000	$ 1,400,000	$ 2,900,000	$ 2,900,000
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	80,400,000		$ 80,400,000		$ 80,400,000
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		$ 1,500,000
Delaware grant obligation	$ 10,469,000		$ 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		31,000
Delaware
Operating Leased Assets [Line Items]
Number of full time employees | employee	328		328		328
Subsequent Event | San Jose, California
Operating Leased Assets [Line Items]
Area of real estate property | ft²						181,000