Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Segment Reporting Information [Line Items]
Net external sales	$ 821,175	$ 968,372	$ 2,770,000	$ 2,760,673
Intersegment sales	77,162	109,516	248,838	328,684
Income (loss) from operations	142,517	117,331	459,120	396,337
Depreciation and amortization	38,424	32,861	109,601	98,244
Other income, net	1,222	1,457	3,676	4,296
Provision for (benefit from) income taxes	38,236	38,131	146,183	129,661
Capital expenditures	94,895	42,645	235,463	111,823
Olefins
Segment Reporting Information [Line Items]
Net external sales	539,785	695,674	1,944,775	1,946,069
Intersegment sales	76,771	109,140	247,671	327,584
Income (loss) from operations	124,452	105,353	409,550	383,376
Depreciation and amortization	27,070	21,746	74,903	64,998
Other income, net	806	949	2,764	2,033
Provision for (benefit from) income taxes	36,092	34,867	130,612	128,405
Capital expenditures	46,867	26,570	92,168	59,969
Vinyls
Segment Reporting Information [Line Items]
Net external sales	281,390	272,698	825,225	814,604
Intersegment sales	391	376	1,167	1,100
Income (loss) from operations	24,059	16,123	67,724	23,565
Depreciation and amortization	11,232	10,967	34,330	32,782
Other income, net	146	(303)	115	179
Provision for (benefit from) income taxes	6,556	5,277	18,989	5,847
Capital expenditures	47,001	15,447	139,836	50,454
Corporate and Other
Segment Reporting Information [Line Items]
Income (loss) from operations	(5,994)	(4,145)	(18,154)	(10,604)
Depreciation and amortization	122	148	368	464
Other income, net	270	811	797	2,084
Provision for (benefit from) income taxes	(4,412)	(2,013)	(3,418)	(4,591)
Capital expenditures	1,027	628	3,459	1,400
Polyethylene | Olefins
Segment Reporting Information [Line Items]
Net external sales	431,614	444,077	1,275,057	1,358,631
Ethylene, Styrene And Other | Olefins
Segment Reporting Information [Line Items]
Net external sales	108,171	251,597	669,718	587,438
PVC, Caustic Soda And Other | Vinyls
Segment Reporting Information [Line Items]
Net external sales	191,310	198,046	569,316	583,214
Building Products | Vinyls
Segment Reporting Information [Line Items]
Net external sales	$ 90,080	$ 74,652	$ 255,909	$ 231,390