Revenue recognition (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Revenue recognition [Abstract]
Receivables, revenue from contracts with customers	$ 98,201		$ 98,201		$ 76,431
Current expected credit losses	90		90		98
Disaggregation of Revenue [Abstract]
Other revenues	56,442	$ 18,389	110,930	$ 29,417
Contract with Customer, Asset and Liability [Abstract]
Contract assets, net - current	6,354		6,354		3,673
Contract assets, net - non-current	32,353		32,353		23,972
Total contract assets, net	38,707		38,707		27,645
Contract liabilities	5,530		5,530		8,399
Revenue recognized in the year from [Abstract]
Amounts included in contract liabilities at the beginning of the year			3,283		6,542
Contract assets net of current expected credit losses	521		521		372
Unbilled receivables net of current expected credit losses	6,640		6,640
Unbilled receivables included in other current assets	356		356
Unbilled receivables included in other non-current asset	6,284		6,284
Capitalized Contract Cost [Abstract]
Capitalized contract costs	11,283		11,283		11,276
Other current assets	604		604		588
Other noncurrent assets	10,679		10,679		$ 10,688
Revenue, Performance Obligation Satisfied over Time [Abstract]
Remaining performance obligation	10,582,799		10,582,799
Development Services [Member]
Disaggregation of Revenue [Abstract]
Other revenues	46,589	17,495	100,660	27,566
Development Services [Member] | Natural Gas Used In Commissioning [Member]
Disaggregation of Revenue [Abstract]
Other revenues	43,771		89,390
Interest Income and Other Revenue [Member]
Disaggregation of Revenue [Abstract]
Other revenues	9,853	$ 894	10,270	$ 1,851
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-07-01
Revenue, Performance Obligation Satisfied over Time [Abstract]
Remaining performance obligation	$ 215,722		$ 215,722
Remaining performance obligation, expected timing of satisfaction, period	6 months		6 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Performance Obligation Satisfied over Time [Abstract]
Remaining performance obligation	$ 514,566		$ 514,566
Remaining performance obligation, expected timing of satisfaction, period	1 year		1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Performance Obligation Satisfied over Time [Abstract]
Remaining performance obligation	$ 515,175		$ 515,175
Remaining performance obligation, expected timing of satisfaction, period	1 year		1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue, Performance Obligation Satisfied over Time [Abstract]
Remaining performance obligation	$ 510,664		$ 510,664
Remaining performance obligation, expected timing of satisfaction, period	1 year		1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-01-01
Revenue, Performance Obligation Satisfied over Time [Abstract]
Remaining performance obligation	$ 503,493		$ 503,493
Remaining performance obligation, expected timing of satisfaction, period	1 year		1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-01-01
Revenue, Performance Obligation Satisfied over Time [Abstract]
Remaining performance obligation	$ 8,323,179		$ 8,323,179
Remaining performance obligation, expected timing of satisfaction, period