Equity Investments (Detail)	6 Months Ended			3 Months Ended		6 Months Ended						6 Months Ended				6 Months Ended
	Jun. 30, 2012 USD ($)	Jul. 02, 2011 USD ($)	Dec. 31, 2011 USD ($)	Jun. 30, 2012 Duferdofin Nucor S.R.L. USD ($)	Jun. 30, 2011 Duferdofin Nucor S.R.L. USD ($)	Jun. 30, 2012 Duferdofin Nucor S.R.L. USD ($)	Jun. 30, 2011 Duferdofin Nucor S.R.L. USD ($)	Jun. 30, 2012 Duferdofin Nucor S.R.L. EUR (€)	Dec. 31, 2011 Duferdofin Nucor S.R.L. USD ($)	Dec. 31, 2011 Duferdofin Nucor S.R.L. EUR (€)	Jun. 30, 2012 Duferdofin Nucor S.R.L. EURO [Member] EUR (€)	Jun. 30, 2012 Duferdofin Nucor S.R.L. Minimum [Member]	Jun. 30, 2012 Duferdofin Nucor S.R.L. Maximum [Member]	Jun. 30, 2012 NuMit [Member] USD ($) BasisPoint	Dec. 31, 2011 NuMit [Member] USD ($)	Jun. 30, 2012 Steel Technologies LLC [Member] USD ($)
Schedule of Equity Method Investments [Line Items]
Equity method investment	$ 729,700,000		$ 775,700,000	$ 433,100,000		$ 433,100,000			$ 493,900,000					$ 272,200,000	$ 259,300,000
Period used for lag basis, in months						1								1
Equity method investment, ownership percentage				50.00%		50.00%								50.00%		100.00%
Equity method investments, share of net assets				46,900,000		46,900,000
Step-up to fair value of certain assets and liabilities				386,200,000		386,200,000
Step-up to fair value of equity method investment, portion related to identification of goodwill						304,000,000
Amortization expense and other purchase accounting adjustments due to fair value step-up	33,122,000	34,680,000		2,800,000	3,200,000	5,600,000	6,100,000
Due from related parties, noncurrent				44.1		44.1		35.0		30.0
Notes receivable, related parties, interest rate												2.34%	3.12%			1.37%
Interest rate per year in excess of Euribor as of date of the notes	1.00%
Equity method investment's credit facilities						Jan. 31, 2016								Oct. 21, 2014
Equity method investment's credit facilities											112,500,000
Total amount outstanding under equity method investment's credit facilities											106,600,000
Number of sheet processing facilities operated by Steel Technologies														24
Investment in joint venture														221,300,000
Notes receivable, related parties																40,000,000
Basis points in excess of LIBOR on note receivable from related party														90
Line of credit extended to joint venture, amount outstanding																87,500,000
Line of credit extended to joint venture																130,000,000
Line of credit facility extended to joint venture, interest rate																1.87%
Amended line of credit extended to joint venture																130,000,000
Line of credit facility, maturity period																2013-04-01
Impairment charge against investment in Duferdofin Nucor	$ 30,000,000