Segment Information - Summarized Balance Sheet Information of Reportable Segments (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Current assets:
Cash and cash equivalents	$ 12.8	$ 27.2	$ 34.6
Trade accounts receivable, net	105.9	88.4
Financing receivable	28.1	28.4
Inventories	125.9	118.2
Prepaid expenses, supplies and other current assets	27.7	24.6
Total current assets	300.4	286.8
Property, plant and equipment, net	290.0	289.2
Equity method investment	7.9	5.0
Identifiable intangible assets, net	10.7	12.5
Goodwill	9.7	42.2
Other noncurrent assets	10.1	9.8
TOTAL ASSETS	628.8	645.5
Current liabilities:
Trade payables	121.2	115.8
Accrued liabilities	36.8	46.4
Total current liabilities	545.7	164.5
Accrued pension benefits	47.5	42.0
Environmental liabilities	11.1	11.6
Other noncurrent liabilities	6.8	6.9
TOTAL LIABILITIES	619.9	586.1
RANA
Current assets:
Goodwill		33.6
RAEU
Current assets:
Goodwill	9.7	8.6
Operating Segments | RANA
Current assets:
Cash and cash equivalents	3.5	11.5
Trade accounts receivable, net	85.6	76.2
Inventories	88.8	79.3
Prepaid expenses, supplies and other current assets	17.4	13.7
Total current assets	195.3	180.7
Property, plant and equipment, net	185.4	195.0
Equity method investment	7.9	5.0
Identifiable intangible assets, net	10.7	12.5
Goodwill		33.6
Other noncurrent assets	6.0	5.0
TOTAL ASSETS	405.3	431.8
Current liabilities:
Trade payables	75.2	73.8
Accrued liabilities	19.7	30.0
Total current liabilities	94.9	103.8
Environmental liabilities	11.1	11.6
Other noncurrent liabilities	4.8	4.5
TOTAL LIABILITIES	110.8	119.9
Operating Segments | RAEU
Current assets:
Cash and cash equivalents	4.8	5.7
Trade accounts receivable, net	20.3	12.2
Financing receivable	28.1	28.4
Inventories	37.1	38.9
Prepaid expenses, supplies and other current assets	9.7	6.4
Total current assets	100.0	91.6
Property, plant and equipment, net	104.6	94.2
Goodwill	9.7	8.6
Other noncurrent assets	3.2	3.5
TOTAL ASSETS	217.5	197.9
Current liabilities:
Trade payables	45.9	41.8
Accrued liabilities	13.9	13.4
Total current liabilities	59.8	55.2
Accrued pension benefits	47.5	42.0
Other noncurrent liabilities	1.8	1.8
TOTAL LIABILITIES	$ 109.1	$ 99.0