Segment Information (Sales) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Segment Reporting Information [Line Items]
Net external sales	$ 1,279,028	$ 1,188,037	$ 3,340,276	$ 3,476,570
Income (loss) from operations	46,563	254,028	428,777	778,682
Depreciation and amortization	94,229	61,248	227,193	180,229
Other income (expense), net	41,265	2,636	52,091	33,790
Provision for (benefit from) income taxes	(6,552)	60,033	129,332	236,824
Capital expenditures	180,170	125,304	467,330	329,236
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net external sales	1,279,028	1,188,037	3,340,276	3,476,570
Capital expenditures	178	1,909	1,579	7,582
Operating Segments [Member] | Olefins [Member]
Segment Reporting Information [Line Items]
Net external sales	497,365	588,097	1,422,869	1,792,052
Income (loss) from operations	118,475	196,703	408,274	608,744
Depreciation and amortization	36,649	27,678	95,582	82,240
Other income (expense), net	1,101	1,323	3,706	3,770
Provision for (benefit from) income taxes	31,956	45,865	136,429	186,534
Capital expenditures	96,469	69,885	285,359	206,719
Operating Segments [Member] | Vinyls [Member]
Segment Reporting Information [Line Items]
Net external sales	781,663	599,940	1,917,407	1,684,518
Income (loss) from operations	22,235	67,779	136,559	202,831
Depreciation and amortization	56,136	33,432	128,691	97,615
Other income (expense), net	(1,226)	10	1,722	6,927
Provision for (benefit from) income taxes	(3,912)	15,812	29,655	55,270
Capital expenditures	83,523	53,510	180,392	114,935
Operating Segments [Member] | Polyethylene [Member] | Olefins [Member]
Segment Reporting Information [Line Items]
Net external sales	380,810	423,631	1,098,500	1,283,545
Operating Segments [Member] | Ethylene, Styrene And Other [Member] | Olefins [Member]
Segment Reporting Information [Line Items]
Net external sales	116,555	164,466	324,369	508,507
Operating Segments [Member] | PVC, Caustic Soda And Other [Member] | Vinyls [Member]
Segment Reporting Information [Line Items]
Net external sales	599,276	468,235	1,492,650	1,315,101
Operating Segments [Member] | Building Products [Member] | Vinyls [Member]
Segment Reporting Information [Line Items]
Net external sales	182,387	131,705	424,757	369,417
Corporate and other [Member]
Segment Reporting Information [Line Items]
Income (loss) from operations	(94,147)	(10,454)	(116,056)	(32,893)
Depreciation and amortization	1,444	138	2,920	374
Other income (expense), net	41,390	1,303	46,663	23,093
Provision for (benefit from) income taxes	(34,596)	(1,644)	(36,752)	(4,980)
Intersegment sales [Member]
Segment Reporting Information [Line Items]
Net external sales	32,744	28,892	88,575	79,752
Intersegment sales [Member] | Olefins [Member]
Segment Reporting Information [Line Items]
Net external sales	30,614	28,551	85,856	78,654
Intersegment sales [Member] | Vinyls [Member]
Segment Reporting Information [Line Items]
Net external sales	$ 2,130	$ 341	$ 2,719	$ 1,098