Basis of Preparation - Balance Sheet Impact (Details) - USD ($) $ in Millions	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets
Accounts receivable, net of allowances	$ 177.3	$ 196.4	$ 196.4
Inventories, net	188.2	162.1	173.7
Unbilled contract revenue	34.2	43.0	36.5
Prepaid expenses	10.2	12.8	14.4
Liabilities
Accounts payable	94.8	105.6	105.4
Customer advances and billings in excess of contract revenue	94.5	99.7	109.6
Other current liabilities	39.5	40.0	39.9
Long-term deferred tax liabilities	55.3	62.7	62.1
Equity
Retained earnings	406.9	366.6	364.3
Balances without adoption of ASC 606
Assets
Accounts receivable, net of allowances	176.5
Inventories, net	207.7		173.7
Unbilled contract revenue	25.6		36.5
Prepaid expenses			14.4
Liabilities
Accounts payable			105.4
Customer advances and billings in excess of contract revenue	110.2		109.6
Other current liabilities	38.3		39.9
Long-term deferred tax liabilities	54.3		62.1
Equity
Retained earnings	403.5		$ 364.3
Adjustments due to ASC 606 | ASU 2014-09
Assets
Accounts receivable, net of allowances	0.8
Inventories, net	(19.5)	(11.6)
Unbilled contract revenue	8.6	6.5
Prepaid expenses		(1.6)
Liabilities
Accounts payable		0.2
Customer advances and billings in excess of contract revenue	(15.7)	(9.9)
Other current liabilities	1.2	0.1
Long-term deferred tax liabilities	1.0	0.6
Equity
Retained earnings	$ 3.4	$ 2.3