Summary of Significant Accounting Policies - Balance Sheet (Details) - USD ($) $ in Millions	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets
Accounts receivable, net	$ 60.1		$ 74.2
Unbilled receivables, net	166.1		138.1
Inventoried costs	48.6		49.0
Liabilities
Accrued expenses	38.7		40.9
Billings in excess of costs and earnings on uncompleted contracts	40.5		42.8
Stockholders’ equity:
Accumulated deficit	729.2		$ 720.8
ASC 606
Assets
Unbilled receivables, net		$ 139.4
Inventoried costs		48.7
Liabilities
Accrued expenses		40.3
Billings in excess of costs and earnings on uncompleted contracts		44.6
Stockholders’ equity:
Accumulated deficit		721.0
ASC 606 | Balances Without Adoption of ASC 606
Assets
Accounts receivable, net	59.6
Unbilled receivables, net	148.3
Inventoried costs	64.1
Liabilities
Billings in excess of costs and earnings on uncompleted contracts	43.2
Stockholders’ equity:
Accumulated deficit	734.7
ASC 606 | Effect of Change Higher/(Lower)
Assets
Accounts receivable, net	0.5
Unbilled receivables, net	17.8
Inventoried costs	(15.5)
Liabilities
Billings in excess of costs and earnings on uncompleted contracts	(2.7)
Stockholders’ equity:
Accumulated deficit	$ (5.5)
Balance at January 1, 2018 | ASC 606
Assets
Unbilled receivables, net		138.1
Inventoried costs		49.0
Liabilities
Accrued expenses		40.9
Billings in excess of costs and earnings on uncompleted contracts		42.8
Stockholders’ equity:
Accumulated deficit		720.8
ASC 606 Adjustment | ASC 606
Assets
Unbilled receivables, net		1.3
Inventoried costs		(0.3)
Liabilities
Accrued expenses		(0.6)
Billings in excess of costs and earnings on uncompleted contracts		1.8
Stockholders’ equity:
Accumulated deficit		$ 0.2