Nature of business and summary of significant accounting policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2019 USD ($) Facility ReportingUnit	Dec. 31, 2018 USD ($) ReportingUnit	Dec. 31, 2017 USD ($)
Accounting Policies [Line Items]
Number of facilities operated | Facility	20
ESOP, plan description	From January 2003 until the Company’s initial public offering of its common stock (IPO) in May 2019, the ESOP owned 100% of the Company’s outstanding shares of common stock which have been fully allocated to active or retired eligible employees.
Percentage of outstanding shares of common stock owned by ESOP	100.00%
Allowance for doubtful accounts receivable	$ 526,000	$ 801,000
Tooling in progress	1,589,000	2,318,000
Depreciation expense	$ 22,296,000	$ 16,372,000	$ 16,975,000
Number of reporting units | ReportingUnit	1	2
Goodwill	$ 71,535,000	$ 69,437,000
Deferred financing costs	142	2,173,000	412,000
Amortization of debt issuance costs and discounts	381,000	198,000	249,000
Accumulated amortization	474	114,000	619,000
Write-offs of debt unamortized costs	154,000	814,000	0
Advertising expense	110,000	116,000	157,000
Topic 606 [Member]
Accounting Policies [Line Items]
Adjustment to retained earnings	0
Mayville Engineering Company, Inc [Member]
Accounting Policies [Line Items]
Goodwill		40,200,000
Defiance Metal Products Co. [Member]
Accounting Policies [Line Items]
Goodwill		29,200,000
Cost of Sales [Member]
Accounting Policies [Line Items]
Depreciation expense	$ 22,296,000	$ 16,372,000	$ 16,975,000