Derivative Financial Instruments - Additional Information (Detail) (USD $)	12 Months Ended							12 Months Ended						12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Apr. 18, 2013	Aug. 01, 2011	Jul. 25, 2011	Dec. 31, 2010 Contract	Jul. 25, 2011 Interest Rate Risk [Member]	Dec. 31, 2010 Minimum [Member]	Dec. 31, 2010 Maximum [Member]	Dec. 31, 2013 Interest Rate Swap [Member] Contract	Dec. 31, 2012 Interest Rate Swap [Member] Contract	Dec. 31, 2013 Natural gas swaps [Member] Contract	Dec. 31, 2012 Natural gas swaps [Member] Contract	Dec. 31, 2011 $1 Billion Credit Facility [Member]	Dec. 31, 2013 $1 Billion Credit Facility [Member]
Derivative Financial Instruments [Line Items]
Interest rate swaps associated with term loan borrowings					$ 500,000,000
Percentage of variable rate debt outstanding							71.00%
Base rate added to applicable margin of borrowings														3.94%
Weighted average fixed rate														3.94% plus the applicable margin on these borrowings
Company's credit facility		925,000,000	925,000,000	1,000,000,000	1,000,000,000										1,000,000,000
Gain (loss) from ineffectiveness	$ 0	$ 0
Derivative contracts held						36				0	0	0	0
Aggregate notional amount of fixed natural gas price swap contracts						1,000,000
Maturity period of fixed natural gas price swap contracts								2011-01	2011-12