Equity Investments - Additional Information (Detail)	9 Months Ended			1 Months Ended			3 Months Ended			9 Months Ended							9 Months Ended		9 Months Ended
	Sep. 28, 2013 USD ($)	Sep. 29, 2012 USD ($)	Dec. 31, 2012 USD ($)	Nov. 30, 2012 Hunter Ridge Energy Services LLC [Member]	Sep. 28, 2013 Hunter Ridge Energy Services LLC [Member] USD ($)	Dec. 31, 2012 Hunter Ridge Energy Services LLC [Member] USD ($)	Sep. 28, 2013 Duferdofin Nucor S.R.L. [Member] USD ($)	Sep. 29, 2012 Duferdofin Nucor S.R.L. [Member] USD ($)	Jun. 30, 2012 Duferdofin Nucor S.R.L. [Member] USD ($)	Sep. 28, 2013 Duferdofin Nucor S.R.L. [Member] USD ($)	Sep. 29, 2012 Duferdofin Nucor S.R.L. [Member] USD ($)	Sep. 28, 2013 Duferdofin Nucor S.R.L. [Member] EUR (€)	Dec. 31, 2012 Duferdofin Nucor S.R.L. [Member] USD ($)	Dec. 31, 2012 Duferdofin Nucor S.R.L. [Member] EUR (€)	Sep. 28, 2013 Duferdofin Nucor S.R.L. [Member] EURO [Member] EUR (€)	Dec. 31, 2012 Duferdofin Nucor S.R.L. [Member] EURO [Member] EUR (€)	Sep. 28, 2013 NuMit [Member] USD ($) Sheet	Dec. 31, 2012 NuMit [Member] USD ($)	Sep. 28, 2013 Steel Technologies LLC [Member] USD ($)	Sep. 28, 2013 Steel Technologies LLC [Member] Maximum [Member]	Sep. 28, 2013 Steel Technologies LLC [Member] Minimum [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment	$ 913,700,000		$ 855,900,000		$ 132,900,000	$ 95,400,000	$ 454,600,000			$ 454,600,000			$ 454,100,000				$ 308,400,000	$ 288,400,000
Period used for lag basis, in months				1 month						1 month							1 month
Equity method investment, ownership percentage				50.00%			50.00%			50.00%							50.00%		100.00%
Equity method investments, share of net assets							50,700,000			50,700,000
Step-up to fair value of certain assets and liabilities							403,900,000			403,900,000
Step-up to fair value of equity method investment, portion related to identification of goodwill							326,200,000
Amortization expense and other purchase accounting adjustments due to fair value step-up	56,051,000	53,518,000					2,800,000	2,700,000		8,500,000	8,300,000
Due from related parties, noncurrent							47,300,000			47,300,000		35,000,000		35,000,000
Notes receivable, related parties, interest rate										1.69%									1.17%
Interest rate per year in excess of Euribor as of date of the notes	1.00%
Equity method investment's credit facilities with parent company, maturity date										Jan. 31, 2016							Oct. 21, 2014
Equity method investment's credit facilities, amount							164,800,000			164,800,000					122,500,000
Total amount outstanding under equity method investment's credit facilities							143,200,000			143,200,000			134,800,000		106,000,000	102,000,000
Line of credit facility, maturity period										Apr. 26, 2016									Apr. 01, 2014
Guarantor obligation percentage of exposure in case of default							50.00%			50.00%
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																			0.90%
Line of credit extended to joint venture, amount outstanding																			16,500,000
Line of credit extended to joint venture																			100,000,000
Line of credit facility extended to joint venture, interest rate																				1.21%	1.20%
Impairment charge against investment in Duferdofin Nucor									$ 30,000,000