Summary of Significant Accounting Policies - Balance Sheet (Details) - USD ($) $ in Millions	Jul. 01, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets
Accounts receivable, net	$ 66.2		$ 74.2
Unbilled receivables, net	160.6
Inventoried costs	49.0		49.0
Liabilities
Accrued expenses	38.4		40.9
Billings in excess of costs and earnings on uncompleted contracts	32.9
Stockholders’ equity:
Accumulated deficit	730.9		$ 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	65.4
Unbilled receivables, net	151.9
Inventoried costs	57.3
Liabilities
Billings in excess of costs and earnings on uncompleted contracts	34.6
Stockholders’ equity:
Accumulated deficit	733.8
ASC 606 | Effect of Change Higher/(Lower)
Assets
Accounts receivable, net	0.8
Unbilled receivables, net	8.7
Inventoried costs	(8.3)
Liabilities
Billings in excess of costs and earnings on uncompleted contracts	(1.7)
Stockholders’ equity:
Accumulated deficit	$ (2.9)
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