Segment Information - Segment Reporting Information (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended	6 Months Ended	9 Months Ended	3 Months Ended		8 Months Ended	9 Months Ended			1 Months Ended	3 Months Ended		8 Months Ended	9 Months Ended	1 Months Ended	3 Months Ended		8 Months Ended	9 Months Ended	1 Months Ended	3 Months Ended		8 Months Ended	9 Months Ended	1 Months Ended	3 Months Ended		8 Months Ended	9 Months Ended	1 Months Ended
	Jun. 30, 2012	Sep. 30, 2012	Jun. 30, 2012	Sep. 30, 2012	Sep. 30, 2012 Successor [Member]	Sep. 30, 2011 Successor [Member]	Sep. 30, 2011 Successor [Member]	Sep. 30, 2012 Successor [Member]	Sep. 30, 2011 Successor [Member]	Dec. 31, 2011 Successor [Member]	Jan. 31, 2011 Predecessor [Member]	Sep. 30, 2012 Minerals [Member] Successor [Member]	Sep. 30, 2011 Minerals [Member] Successor [Member]	Sep. 30, 2011 Minerals [Member] Successor [Member]	Sep. 30, 2012 Minerals [Member] Successor [Member]	Jan. 31, 2011 Minerals [Member] Predecessor [Member]	Sep. 30, 2012 Pigment [Member] Successor [Member]	Sep. 30, 2011 Pigment [Member] Successor [Member]	Sep. 30, 2011 Pigment [Member] Successor [Member]	Sep. 30, 2012 Pigment [Member] Successor [Member]	Jan. 31, 2011 Pigment [Member] Predecessor [Member]	Sep. 30, 2012 Corporate and Other Successor [Member]	Sep. 30, 2011 Corporate and Other Successor [Member]	Sep. 30, 2011 Corporate and Other Successor [Member]	Sep. 30, 2012 Corporate and Other Successor [Member]	Jan. 31, 2011 Corporate and Other Predecessor [Member]	Sep. 30, 2012 Intersegment Elimination Successor [Member]	Sep. 30, 2011 Intersegment Elimination Successor [Member]	Sep. 30, 2011 Intersegment Elimination Successor [Member]	Sep. 30, 2012 Intersegment Elimination Successor [Member]	Jan. 31, 2011 Intersegment Elimination Predecessor [Member]
Segment Reporting Information [Line Items]
Net Sales		$ 216.1		$ 255.6	$ 487.3	$ 465.4	$ 1,160.8	$ 1,349.8	$ 1,160.8		$ 107.6	$ 271.7	$ 44.0	$ 107.9	$ 443.6	$ 7.6	$ 279.8	$ 399.4	$ 1,002.2	$ 990.1	$ 88.5	$ 38.6	$ 37.5	$ 93.3	$ 96.6	$ 14.5	$ (102.8)	$ (15.5)	$ (42.6)	$ (180.5)	$ (3.0)
Income (Loss) from operations		(24.5)		(21.2)	(38.1)	99.2	201.8	95.4	201.8		19.9	19.4	13.3	24.3	110.4	1.9	(13.2)	111.6	219.4	137.4	20.3	(25.6)	(25.7)	(41.3)	(129.7)	(1.4)	(18.7)		(0.6)	(22.7)	(0.9)
Interest and debt expense					(18.1)	(8.0)	(21.5)	(39.0)	(21.5)		(2.9)
Other income					0.2	(1.3)	(1.7)	(4.8)	(1.7)		1.6
Gain on bargain purchase	202.3		1,061.1					1,045.6
Reorganization income											613.6
Income (Loss) from Continuing Operations before Income Taxes					(56.0)	89.9	178.6	1,097.2	178.6		632.2
Total Assets					5,665.9	1,587.9	1,587.9	5,665.9	1,587.9	1,657.4	1,448.1	3,128.4	224.8	224.8	3,128.4	221.0	1,710.0	1,154.1	1,154.1	1,710.0	987.2	858.4	211.0	211.0	858.4	241.3	(30.9)	(2.0)	(2.0)	(30.9)	(1.4)
Depreciation, Depletion and Amortization					67.3	22.6	56.8	120.2			4.1	43.1	4.2	11.7	58.7	0.6	20.1	14.6	36.1	50.7	2.7	4.1	3.8	9.0	10.8	0.8
Capital Expenditures					$ 43.7	$ 13.6	$ 120.7	$ 91.2			$ 5.5	$ 27.2	$ 2.8	$ 5.4	$ 46.7		$ 9.8	$ 6.0	$ 104.6	$ 25.2	$ 4.2	$ 6.7	$ 4.8	$ 10.7	$ 19.3	$ 1.3