BUSINESS COMBINATION - Cash Proceeds (Details) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended	3 Months Ended		12 Months Ended
	Feb. 27, 2017	Feb. 28, 2018	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019
Proceeds from issuance of common stock		$ 84.4			$ 84.4	$ 127.9
Proceeds from Term Loan Facility					$ 6.1	$ 12.3
Common stock shares sold (in shares)					64,455,174		64,589,075
Common stock shares outstanding					64,455,174		64,589,075
Shares outstanding value (par value)					$ 0.0001		$ 0.0001
Hennessy Capital Acquisition Corp II and HCAC Merger Sub Inc
Proceeds from issuance of common stock	$ 83.4
Issuance of convertible preferred stock	65.0
Proceeds from Term Loan Facility	250.0
Cash(2)	3.2
Total proceeds	401.6
Payment of deferred financing fees (7)	14.1
Hennessy transaction costs	19.1
Daseke transaction costs(9)	1.2		$ 0.4	$ 0.8
Total use of proceeds	367.0
Net cash received	$ 34.6
Common stock shares sold (in shares)	37,715,960
Common stock shares outstanding	37,715,960
Hennessy Capital Acquisition Corp II and HCAC Merger Sub Inc | Main Street Capital Corporation and Prudential Capital Partners
Repayment of debt	$ 36.2
Hennessy Capital Acquisition Corp II and HCAC Merger Sub Inc | Interest Expense
Excludes fees paid subsequent to closing	81.0
Hennessy Capital Acquisition Corp II and HCAC Merger Sub Inc | Line of credit
Repayment of debt	16.7
Hennessy Capital Acquisition Corp II and HCAC Merger Sub Inc | Line of credit | Interest Expense
Payment of accrued interest	59.0
Hennessy Capital Acquisition Corp II and HCAC Merger Sub Inc | Senior term loan
Repayment of debt	122.7
Hennessy Capital Acquisition Corp II and HCAC Merger Sub Inc | Senior term loan | Interest Expense
Payment of accrued interest	422.0
Hennessy Capital Acquisition Corp II and HCAC Merger Sub Inc | Equipment term loans
Repayment of debt	89.5
Hennessy Capital Acquisition Corp II and HCAC Merger Sub Inc | Equipment term loans | Interest Expense
Payment of accrued interest	731.0
Hennessy Capital Acquisition Corp II and HCAC Merger Sub Inc | Subordinated notes
Repayment of debt	67.5
Hennessy Capital Acquisition Corp II and HCAC Merger Sub Inc | Subordinated notes | Interest Expense
Payment of accrued interest	$ 745.0
IPO | Hennessy Capital Acquisition Corp II and HCAC Merger Sub Inc
Common stock shares sold (in shares)	8,342,918