Summary of Significant Accounting Policies - Risk (Details)	12 Months Ended
Dec. 31, 2020
Warranty Costs
Labor warranty period after servicing of existing MEP system	30 days
Revenue \| Customer concentration \| Minimum
Warranty Costs
Single customer, percentage of revenue	5.00%

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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