Equity Investments - Additional Information (Detail)	9 Months Ended			1 Months Ended		3 Months Ended		6 Months Ended	9 Months Ended					9 Months Ended						9 Months Ended		9 Months Ended
	Oct. 04, 2014 USD ($)	Sep. 28, 2013 USD ($)	Dec. 31, 2013 USD ($)	Oct. 04, 2014 Hunter Ridge Energy Services LLC [Member] USD ($)	Dec. 31, 2013 Hunter Ridge Energy Services LLC [Member] USD ($)	Oct. 04, 2014 Duferdofin Nucor S.r.l. [Member] USD ($)	Sep. 28, 2013 Duferdofin Nucor S.r.l. [Member] USD ($)	Jun. 30, 2012 Duferdofin Nucor S.r.l. [Member] USD ($)	Oct. 04, 2014 Duferdofin Nucor S.r.l. [Member] USD ($)	Sep. 28, 2013 Duferdofin Nucor S.r.l. [Member] USD ($)	Oct. 04, 2014 Duferdofin Nucor S.r.l. [Member] EUR (€)	Dec. 31, 2013 Duferdofin Nucor S.r.l. [Member] USD ($)	Dec. 31, 2013 Duferdofin Nucor S.r.l. [Member] EUR (€)	Oct. 04, 2014 Duferdofin Nucor S.r.l. [Member] Standby Medium Long Term Credit Facility [Member] USD ($)	Oct. 04, 2014 Duferdofin Nucor S.r.l. [Member] Standby Medium Long Term Credit Facility [Member] EUR (€)	Oct. 04, 2014 Duferdofin Nucor S.r.l. [Member] Facility A [Member] USD ($)	Oct. 04, 2014 Duferdofin Nucor S.r.l. [Member] Facility A [Member] EUR (€)	Dec. 31, 2013 Duferdofin Nucor S.r.l. [Member] Facility A [Member] USD ($)	Dec. 31, 2013 Duferdofin Nucor S.r.l. [Member] Facility A [Member] EUR (€)	Oct. 04, 2014 NuMit LLC [Member] USD ($)	Dec. 31, 2013 NuMit LLC [Member] USD ($)	Oct. 04, 2014 Steel Technologies LLC [Member] USD ($) Sheet	Oct. 04, 2014 Steel Technologies LLC [Member] Notes Receivable One [Member] USD ($)	Oct. 04, 2014 Steel Technologies LLC [Member] Notes Receivable Two [Member]	May 02, 2014 Steel Technologies LLC [Member] Notes Receivable Two [Member] USD ($)
Schedule of Equity Method Investments [Line Items]
Equity method investment	$ 923,200,000		$ 936,000,000	$ 137,900,000	$ 134,500,000	$ 431,000,000			$ 431,000,000			$ 465,400,000								$ 334,900,000	$ 318,400,000
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%
Equity method investments, share of net assets						58,900,000			58,900,000
Basis difference due to the step-up to fair value of certain assets and liabilities						372,100,000			372,100,000
Step-up to fair value of equity method investment, portion related to identification of goodwill									302,200,000
Amortization expense and other purchase accounting adjustments due to fair value step-up	54,127,000	56,051,000				2,600,000	2,800,000		8,000,000	8,500,000
Due from related parties, noncurrent						43,800,000			43,800,000		35,000,000	48,200,000	35,000,000
Notes receivable, related parties, interest rate									1.34%														1.13%	1.44%
Interest rate per year in excess of Euribor as of date of the notes									1.00%
Equity method investments note payable with parent company, maturity date									Jan. 31, 2016															May 01, 2015
Equity method investments credit facilities, amount																	122,500,000
Total amount outstanding under equity method investments credit facilities														75,100,000	60,000,000	131,400,000	105,000,000	154,400,000	112,000,000
Line of credit facility, maturity period														Apr. 22, 2016	Apr. 22, 2016	Apr. 26, 2016	Apr. 26, 2016					Apr. 01, 2015
Guarantor obligation percentage of exposure in case of default														50.00%	50.00%	50.00%	50.00%
Equity method investment, ownership percentage																						100.00%
Number of sheet processing facilities operated by Steel Technologies																						25
Notes receivable, related parties																							40,000,000		44,000,000
Basis points in excess of LIBOR on note receivable from related party																							0.90%
Line of credit extended to joint venture																						60,000,000
Line of credit extended to joint venture, amount outstanding																						8,500,000
Line of credit extended to joint venture, interest rate																						1.34%
Impairment of equity method investments								$ 30,000,000