Debtor-In-Possession Financial Information - Balance Sheet (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 24.9	$ 27.2	$ 35.7
Trade accounts receivable, net	122.5	88.4
Inventories	107.3	118.2
Prepaid expenses, supplies and other current assets	33.9	24.6
Total current assets	305.1	286.8
Property, plant and equipment, net	247.5	289.2
Equity method investment	7.9	5.0
Deferred income taxes, net	9.0
Other noncurrent assets	12.8	9.8
TOTAL ASSETS	592.1	645.5
Current liabilities:
Trade payables	96.4	115.8
Accrued liabilities	28.1	46.4
RA DIP Financing, net	103.9
Long-term debt due within one year, net	3.6	2.3
Total current liabilities	232.0	164.5
Environmental liabilities	10.4	11.6	11.7
Long-term debt, net	4.4	354.2
Other noncurrent liabilities	7.4	6.9
Liabilities not subject to compromise	303.8	586.1
Liabilities subject to compromise	340.7
TOTAL LIABILITIES	644.5	586.1
Redeemable Preferred Stock	28.5	24.9	21.9
Stockholders' deficit:
Accumulated other comprehensive loss	4.5	(7.1)	(1.0)
TOTAL STOCKHOLDERS' EQUITY (DEFICIT)	(80.9)	34.5	$ 142.4	$ 85.6
TOTAL LIABILITIES, REDEEMABLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT)	592.1	$ 645.5
Debtors
Current assets:
Cash and cash equivalents	7.6
Trade accounts receivable, net	83.9
Inventories	54.0
Prepaid expenses, supplies and other current assets	24.4
Total current assets	169.9
Property, plant and equipment, net	109.7
Equity method investment	7.9
Deferred income taxes, net	8.9
Investment in subsidiaries	60.8
Intercompany receivable	92.3
Other noncurrent assets	7.8
TOTAL ASSETS	457.3
Current liabilities:
Trade payables	48.4
Accrued liabilities	13.2
RA DIP Financing, net	103.9
Long-term debt due within one year, net	2.0
Total current liabilities	167.5
Environmental liabilities	4.7
Long-term debt, net	2.3
Other noncurrent liabilities	5.4
Liabilities not subject to compromise	179.9
Liabilities subject to compromise	340.7
TOTAL LIABILITIES	520.6
Redeemable Preferred Stock	28.5
Stockholders' deficit:
Paid-in-capital and accumulated deficit	(80.6)
Accumulated other comprehensive loss	(11.2)
TOTAL STOCKHOLDERS' EQUITY (DEFICIT)	(91.8)
TOTAL LIABILITIES, REDEEMABLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT)	$ 457.3