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Accounting policies - Additional Information (Details) - USD ($)		3 Months Ended		6 Months Ended
	Jan. 24, 2020	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Foreign Currency Transaction Gain (Loss), before Tax [Abstract]
Foreign Currency Transaction Gain (Loss), before Tax		$ (370,315)	$ (45,666)	$ (189,330)	$ 12,035
Contracts in progress
Unsatisfied or partially unsatisfied performance obligations for contracts in progress		3,000,000.0		3,000,000.0
Revenue expected to earn as it satisfies its performance obligations during the remainder of the year ending December 31, 2020		1,400,000		1,400,000
Revenue expected to earn as it satisfies its performance obligations after year ending December 31, 2020		1,600,000		$ 1,600,000
Aerex
Contracts in progress
Ownership interest acquired	49.00%
Cash	$ 8,500,000
Ownership interest held	100.00%
Minimum [Member]
Contracts in progress
Number of days after consumption billings are collected				30 days
Maximum [Member]
Contracts in progress
Number of days after consumption billings are collected				35 days
Bahamas [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Deposits held in foreign bank		9,800,000		$ 9,800,000
Certificates of Deposit [Member]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash Equivalents, at Carrying Value		9,100,000		9,100,000		$ 12,700,000
Cash Equivalents, at Carrying Value		$ 9,100,000		$ 9,100,000		$ 12,700,000