Summary of Significant Accounting Policies - Impact of ASC 326 (Details) - USD ($) $ in Millions	Sep. 30, 2020	Jan. 01, 2020	Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on Accounts receivable and retention	$ 4.1	$ 0.3	$ 0.6
Allowance for credit losses on Other receivables		1.6
Allowance for credit losses on costs and estimated earnings in excess of billings on uncompleted contracts		0.0
Total		1.9
As Reported under ASC 326
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on Accounts receivable and retention		1.6
Allowance for credit losses on Other receivables		4.2
Allowance for credit losses on costs and estimated earnings in excess of billings on uncompleted contracts		0.1
Total		5.9
ASU 2016-13 | Impact of ASC 326 Adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses on Accounts receivable and retention		1.3
Allowance for credit losses on Other receivables		2.6
Allowance for credit losses on costs and estimated earnings in excess of billings on uncompleted contracts		0.1
Total		$ 4.0