Equity and Other Investments - Schedule of Combined Financial Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended			3 Months Ended	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Mar. 31, 2013 OCI LP and OCI Co [Member]	Jun. 30, 2013 OCI LP and OCI Co [Member]
Schedule Of Results Related To Equity Accounted Investees [Line Items]
Net sales						$ 79,822	$ 157,882
Gross profit						22,372	43,315
Net income	41,065	49,938	88,971	101,247		18,589	36,958
Income allocation to NRP's equity interests						8,565	16,161
Current assets	152,893		152,893		196,195		151,741
Property, plant and equipment	29,268		29,268		32,401		191,051
Other assets	560		560		630		24
Total assets	1,975,851		1,975,851		1,764,672		342,816
Current liabilities	87,384		87,384		117,815		34,286
Long term debt	1,088,556		1,088,556		897,039		46,000
Other liabilities							3,665
Capital	658,306		658,306		617,447		258,865
Total liabilities and partners' capital	1,975,851		1,975,851		1,764,672		342,816
Net book value of NRP's equity interests							139,347
Excess of NRP's investment over net book value of NRP's equity interests	$ 78,700		$ 78,700				$ 140,530