Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Segment Reporting Information [Line Items]
Net external sales	$ 1,086,061	$ 1,185,002	$ 2,061,248	$ 2,288,533
Income (loss) from operations	179,938	295,374	382,214	524,654
Depreciation and amortization	67,250	60,340	132,964	118,981
Other income (expense), net	8,181	22,058	10,826	31,154
Provision for (benefit from) income taxes	66,584	98,413	135,884	176,791
Capital expenditures	150,833	108,110	287,160	203,933
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net external sales	1,086,061	1,185,002	2,061,248	2,288,533
Operating Segments [Member] | Olefins [Member]
Segment Reporting Information [Line Items]
Net external sales	494,484	620,878	925,504	1,203,955
Income (loss) from operations	140,564	220,938	289,799	412,041
Depreciation and amortization	30,236	27,623	58,933	54,562
Other income (expense), net	1,093	(104)	2,606	2,448
Provision for (benefit from) income taxes	51,940	74,212	104,473	140,669
Capital expenditures	93,739	81,534	188,890	136,835
Operating Segments [Member] | Vinyls [Member]
Segment Reporting Information [Line Items]
Net external sales	591,577	564,124	1,135,744	1,084,578
Income (loss) from operations	52,208	87,966	114,324	135,052
Depreciation and amortization	36,268	32,599	72,555	64,183
Other income (expense), net	4,466	1,413	2,949	6,916
Provision for (benefit from) income taxes	16,297	26,653	33,567	39,458
Capital expenditures	56,613	24,569	96,869	61,425
Operating Segments [Member] | Corporate and Other
Segment Reporting Information [Line Items]
Capital expenditures	481	2,007	1,401	5,673
Operating Segments [Member] | Polyethylene | Olefins [Member]
Segment Reporting Information [Line Items]
Net external sales	371,658	450,482	717,690	859,914
Operating Segments [Member] | Ethylene, Styrene And Other | Olefins [Member]
Segment Reporting Information [Line Items]
Net external sales	122,826	170,396	207,814	344,041
Operating Segments [Member] | PVC, Caustic Soda And Other | Vinyls [Member]
Segment Reporting Information [Line Items]
Net external sales	462,472	429,878	893,374	846,866
Operating Segments [Member] | Building Products | Vinyls [Member]
Segment Reporting Information [Line Items]
Net external sales	129,105	134,246	242,370	237,712
Corporate, Non-Segment [Member] | Corporate and Other
Segment Reporting Information [Line Items]
Income (loss) from operations	(12,834)	(13,530)	(21,909)	(22,439)
Depreciation and amortization	746	118	1,476	236
Other income (expense), net	2,622	20,749	5,271	21,790
Provision for (benefit from) income taxes	(1,653)	(2,452)	(2,156)	(3,336)
Intersegment sales [Member]
Segment Reporting Information [Line Items]
Net external sales	27,518	27,028	55,831	50,860
Intersegment sales [Member] | Olefins [Member]
Segment Reporting Information [Line Items]
Net external sales	27,293	26,641	55,242	50,103
Intersegment sales [Member] | Vinyls [Member]
Segment Reporting Information [Line Items]
Net external sales	$ 225	$ 387	$ 589	$ 757