Nature of Operations (Details) $ / shares in Units, $ in Thousands			1 Months Ended								3 Months Ended			12 Months Ended
	Apr. 13, 2020 USD ($)	Mar. 08, 2018 USD ($)	Jan. 31, 2020 shares	Dec. 31, 2019 USD ($) $ / shares shares	Nov. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)	Apr. 30, 2019 USD ($)	Mar. 31, 2019 USD ($) $ / shares shares	Nov. 30, 2018 USD ($) $ / shares shares	Mar. 31, 2018 USD ($)	Mar. 31, 2020 USD ($) item $ / shares	Dec. 31, 2019 USD ($) $ / shares shares	Mar. 31, 2019 USD ($) item $ / shares	Dec. 31, 2019 USD ($) $ / shares shares	May 06, 2020 USD ($)	May 05, 2020
Liquidity
Number of fuel cell systems deployed | item													32,000
Net loss attributable to common shareholders											$ 37,492		$ 31,004
Accumulated deficit				$ 1,345,807							1,383,299	$ 1,345,807		$ 1,345,807
Net cash used in operating activities											60,015		36,263
Net loss attributable to the Company											(37,479)		(30,952)
Net outflows from fluctuations in working capital and other assets and liabilities											33,900
Non-cash charges											11,400
Cash and cash equivalents				139,496							74,340	139,496		139,496
Net working capital				162,500							125,400	$ 162,500		162,500
Net cash used in investing activities											(6,355)		(2,274)
Net cash provided by financing activities											4,083		37,650
Proceeds from exercise of stock options											6,100
Increase in cash flows from new finance obligations											9,000
Principal payments on long-term debt											5,315		17,153
Proceeds from public offerings, net of transaction costs													23,498
Value of shares issued													23,498
Net proceeds											9,024
Additional loan															$ 50,000
Principal amount										$ 100,000
Interest rate (as a percent)															9.50%	12.00%
Remaining lease payments											268,100
Security on lease											234,600
Letter of credit											101,600
Repayments of finance obligations											5,730		$ 53,534
Number of common stock sold | shares								10,000,000
Share price (in dollars per share) | $ / shares								$ 2.35					$ 2.35
Number of shares of common stock issued on conversion of preferred stock | shares			216,000									13,800,000
Number of preferred shares that had been converted to common stock | shares			500									30,962
Subsequent event
Liquidity
Incremental term loan															$ 50,000
Additional loan															$ 50,000
Interest rate (as a percent)															9.50%	12.00%
Secured term loan facility
Liquidity
Proceeds from borrowing of long-term debt					$ 20,000
Wells Fargo
Liquidity
Remaining lease payments											108,000
Letter of credit											$ 55,500
Sale/leaseback transactions under Wells Fargo MLA | item											0
Financial Institutions
Liquidity
Remaining lease payments											$ 160,100
Cash collateral for unguaranteed portions											179,100
Loan and security agreement | Secured term loan facility | Subsequent event
Liquidity
Incremental term loan															$ 50,000
Additional loan															$ 50,000
Interest rate (as a percent)															9.50%	12.00%
Loan and security agreement | Generate Lending, LLC
Liquidity
Termination of certain equipment leases								$ 50,300
Repayments of finance obligations								17,600
Loan and security agreement | Generate Lending, LLC | Secured term loan facility
Liquidity
Proceeds from borrowing of long-term debt							$ 15,000	85,000
Outstanding balance											107,500
Proceeds from borrowing of long-term debt, net of transaction costs								85,000
Principal amount								100,000					$ 100,000
Interest rate (as a percent)					12.00%
Convertible Senior Notes
Liquidity
Principal amount						$ 40,000
Interest rate (as a percent)						7.50%
$40M Convertible Senior Note
Liquidity
Net proceeds						$ 39,100
Outstanding balance											40,400
Proceeds from borrowing of long-term debt, net of transaction costs						39,100
Principal amount				48,000		$ 40,000					$ 48,000	$ 48,000		48,000
Interest rate (as a percent)						7.50%
Obligation, net of interest accretion						$ 48,000
Share price (in dollars per share) | $ / shares											$ 3.54
$100M Convertible Senior Notes
Liquidity
Net proceeds		$ 52,356								95,900
Outstanding balance											$ 72,600
Principal amount		100,000		$ 100,000		$ 1,000				$ 100,000	$ 100,000	$ 100,000		$ 100,000
Interest rate (as a percent)										5.50%
Purchase of capped call and common stock forward		$ 43,500								$ 43,500
Share price (in dollars per share) | $ / shares											$ 3.54
Series E Preferred Stock
Liquidity
Number of redeemed shares | shares														4,038
Number of preferred shares that had been converted to common stock | shares			500
Series E Redeemable Convertible Preferred Stock
Liquidity
Shares issued (in shares) | shares									35,000
Redeemable stock issued, stated value (in dollars per share) | $ / shares				$ 0.01					$ 0.01		$ 0.01	$ 0.01		$ 0.01
Aggregate proceeds from issuance of preferred stock									$ 30,900
Number of redeemed shares | shares												4,038
Amount of redeemed shares												$ 4,000
At Market Issuance Sales Agreement
Liquidity
Authorized amount	$ 75,000
Public Offerings
Liquidity
Proceeds from public offerings, net of transaction costs				$ 120,400				$ 23,500
Number of common stock sold | shares				46,000,000				10,000,000
Share price (in dollars per share) | $ / shares				$ 2.75				$ 2.35				$ 2.75	$ 2.35	$ 2.75