Segment Reporting Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Segment Reporting Information [Line Items]
Net external sales	$ 913,958	$ 925,049	$ 1,948,825	$ 1,792,301
Intersegment sales	69,831	112,578	171,676	219,168
Income (loss) from operations	170,978	138,369	316,603	279,006
Depreciation and amortization	35,783	32,805	71,177	65,383
Other income, net	1,107	1,632	2,454	2,839
Provision for (benefit from) income taxes	60,965	46,150	107,947	91,530
Capital expenditures	75,666	38,523	140,568	69,178
Olefins
Segment Reporting Information [Line Items]
Net external sales	672,719	645,315	1,404,990	1,250,395
Intersegment sales	69,443	112,174	170,900	218,444
Income (loss) from operations	155,891	132,767	285,098	278,023
Depreciation and amortization	24,070	21,608	47,833	43,252
Other income, net	1,001	904	1,957	1,084
Provision for (benefit from) income taxes	52,345	45,247	94,520	93,538
Capital expenditures	27,821	15,450	45,302	33,399
Vinyls
Segment Reporting Information [Line Items]
Net external sales	241,239	279,734	543,835	541,906
Intersegment sales	388	404	776	724
Income (loss) from operations	22,583	10,290	43,665	7,442
Depreciation and amortization	11,589	11,041	23,098	21,815
Other income, net	(272)	(30)	(31)	481
Provision for (benefit from) income taxes	6,417	2,723	12,433	570
Capital expenditures	45,994	22,376	92,834	35,007
Corporate and Other
Segment Reporting Information [Line Items]
Income (loss) from operations	(7,496)	(4,688)	(12,160)	(6,459)
Depreciation and amortization	124	156	246	316
Other income, net	378	758	528	1,274
Provision for (benefit from) income taxes	2,203	(1,820)	994	(2,578)
Capital expenditures	1,851	697	2,432	772
Polyethylene | Olefins
Segment Reporting Information [Line Items]
Net external sales	398,023	467,851	843,443	914,554
Ethylene, Styrene And Other | Olefins
Segment Reporting Information [Line Items]
Net external sales	274,696	177,464	561,547	335,841
PVC, Caustic Soda And Other | Vinyls
Segment Reporting Information [Line Items]
Net external sales	163,623	193,311	378,006	385,168
Building Products | Vinyls
Segment Reporting Information [Line Items]
Net external sales	$ 77,616	$ 86,423	$ 165,829	$ 156,738