Segment Information (Details 2) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2013
Operating income (loss)
Corporate SG & A	$ (82,371)	$ (80,240)	$ (241,381)	$ (223,745)
Profit sharing	(9,008)	(12,865)	(18,637)	(28,729)
Operating income (loss)	131,029	188,643	308,359	401,480
Assets
Cash and equivalents	473,790	159,591	473,790	159,591	$ 419,401	$ 361,363	$ 357,490	$ 395,156
Accounts receivable	757,110		757,110			859,835
Inventories	1,321,397		1,321,397			1,618,419
Deferred income taxes	28,839		28,839			35,503
Property, plant and equipment, net	3,013,659		3,013,659			3,123,906
Other	83,283		83,283			97,529
Total assets	6,842,541	7,578,283	6,842,541	7,578,283		7,311,027
Liabilities
Accounts payable	386,370		386,370			511,056
Income taxes payable	14,246		14,246			6,086
Accrued interest	47,998		47,998			50,405
Debt	2,600,000		2,600,000			3,000,000
Deferred income taxes	576,674		576,674			$ 542,033
Liabilities	3,886,756	4,540,294	3,886,756	4,540,294
Severstal Columbus LLC
Acquisition
Acquisition and related costs		25,000		25,000
Operating Segment | Other
Operating income (loss)
Corporate SG & A	(9,500)	(12,400)	(27,100)	(31,700)
Company-wide equity- based compensation	(5,300)	(5,100)	(17,500)	(14,400)
Profit sharing	(7,500)	(11,600)	(14,400)	(25,200)
Other, net	(2,000)	(3,200)	(8,000)	(8,200)
Operating income (loss)	(28,401)	(42,960)	(117,273)	(129,260)
Assets
Cash and equivalents	415,700	82,900	415,700	82,900
Accounts receivable	30,000	51,300	30,000	51,300
Inventories	36,800	114,600	36,800	114,600
Deferred income taxes	28,800	18,300	28,800	18,300
Property, plant and equipment, net	309,600	572,900	309,600	572,900
Debt issuance costs, net	34,400	39,900	34,400	39,900
Intra-company debt	6,500	7,400	6,500	7,400
Other	37,000	41,700	37,000	41,700
Total assets	898,772	929,041	898,772	929,041
Liabilities
Accounts payable	109,800	165,000	109,800	165,000
Income taxes payable	14,700	26,900	14,700	26,900
Accrued interest	47,800	21,100	47,800	21,100
Accrued profit sharing	14,500	25,200	14,500	25,200
Debt	2,641,300	3,054,900	2,641,300	3,054,900
Deferred income taxes	68,000	100,600	68,000	100,600
Other	27,200	42,400	27,200	42,400
Liabilities	2,923,253	3,436,135	2,923,253	3,436,135
Operating Segment | Other | MINNESOTA
Operating income (loss)
Operating income (loss)	$ (4,100)	$ (10,700)	$ (50,300)	$ (49,800)