Investment in Affiliate and Other Assets - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended			1 Months Ended	3 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Apr. 30, 2014	Dec. 31, 2012	Sep. 30, 2012
Other Assets Non Current [Line Items]
Net sales	$ 432.0	$ 476.5	$ 491.7	$ 462.4	$ 400.1	$ 448.2	$ 516.1	$ 499.2	$ 1,862.6	$ 1,863.6	$ 2,087.3
Income (loss) from continuing operations before income taxes									112.0	(217.9)	301.4
Net income (loss)	13.7	37.5	23.7	4.6	10.8	(40.9)	(48.6)	(48.2)	79.5	(126.9)	222.1
Capitalized operating permits, net of amortization	53.2				59.5				53.2	59.5
Assets held for sale write-down											1.2
Loss on sale									0.9	0.5	(1.5)
Collateral Trust
Other Assets Non Current [Line Items]
Decrease in restricted cash												18.0
Capitalized Operating Permit Costs
Other Assets Non Current [Line Items]
Amortization of capitalized operating permit costs									6.6	6.5	4.9
Capitalized operating permits, net of amortization	25.3				18.8				25.3	18.8
Capitalized Operating Permit Costs | Permits Subject to Amortization
Other Assets Non Current [Line Items]
Amortization of capitalized operating permit, 2015	6.3								6.3
Amortization of capitalized operating permit, 2016	6.3								6.3
Amortization of capitalized operating permit, 2017	6.3								6.3
Amortization of capitalized operating permit, 2018	6.3								6.3
Amortization of capitalized operating permit, 2019	6.3								6.3
Basic Management Inc And Landwell
Other Assets Non Current [Line Items]
Net sales					15.9
Income (loss) from continuing operations before income taxes					6.9
Net income (loss)					5.3
BMI
Other Assets Non Current [Line Items]
Equity ownership percentage					32.00%					32.00%
LandWell
Other Assets Non Current [Line Items]
Equity ownership percentage					12.00%					12.00%
LandWell | General Partner
Other Assets Non Current [Line Items]
Indirect controlling interest in subsidiary					50.00%					50.00%
LPC
Other Assets Non Current [Line Items]
Purchase of TiO2 from the plant											52.00%
Net sales									386.9	449.1	477.7
CompX
Other Assets Non Current [Line Items]
Number of facilities held for sale											2
Assets held for sale write-down														0.4
Net proceeds of sale										1.6			3.6
Loss on sale													$ 0.8