Segment Information (Sales) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Segment Reporting Information [Line Items]
Net external sales	$ 1,942,616	$ 975,187
Income (loss) from operations	235,298	202,276
Depreciation and amortization	150,269	65,714
Other income (expense), net	5,071	2,645
Provision for (benefit from) income taxes	55,883	69,300
Capital expenditures	134,285	136,328
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net external sales	1,942,616	975,187
Operating Segments [Member] | Olefins [Member]
Segment Reporting Information [Line Items]
Net external sales	542,995	431,020
Income (loss) from operations	179,817	149,235
Depreciation and amortization	41,040	28,697
Other income (expense), net	1,370	1,513
Provision for (benefit from) income taxes	57,811	52,533
Capital expenditures	25,350	95,152
Operating Segments [Member] | Vinyls [Member]
Segment Reporting Information [Line Items]
Net external sales	1,399,621	544,167
Income (loss) from operations	71,441	62,116
Depreciation and amortization	107,273	36,287
Other income (expense), net	3,878	(1,519)
Provision for (benefit from) income taxes	14,958	17,270
Capital expenditures	108,081	40,256
Operating Segments [Member] | Polyethylene [Member] | Olefins [Member]
Segment Reporting Information [Line Items]
Net external sales	385,942	346,032
Operating Segments [Member] | Styrene, Feedstock And Other [Member] | Olefins [Member]
Segment Reporting Information [Line Items]
Net external sales	157,053	84,988
Operating Segments [Member] | PVC, Caustic Soda And Other [Member] | Vinyls [Member]
Segment Reporting Information [Line Items]
Net external sales	1,131,129	430,902
Operating Segments [Member] | Building Products [Member] | Vinyls [Member]
Segment Reporting Information [Line Items]
Net external sales	268,492	113,265
Corporate and other [Member]
Segment Reporting Information [Line Items]
Income (loss) from operations	(15,960)	(9,075)
Depreciation and amortization	1,956	730
Other income (expense), net	(177)	2,651
Provision for (benefit from) income taxes	(16,886)	(503)
Capital expenditures	854	920
Intersegment sales [Member]
Segment Reporting Information [Line Items]
Net external sales	86,236	28,313
Intersegment sales [Member] | Olefins [Member]
Segment Reporting Information [Line Items]
Net external sales	85,944	27,949
Intersegment sales [Member] | Vinyls [Member]
Segment Reporting Information [Line Items]
Net external sales	$ 292	$ 364