Subsequent Events - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended		19 Months Ended			3 Months Ended	12 Months Ended		1 Months Ended	3 Months Ended	0 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012	Dec. 31, 2012 9 3/4% Senior Secured Notes Due 2015 [Member]	Nov. 15, 2009 9 3/4% Senior Secured Notes Due 2015 [Member]	Jun. 30, 2011 Inventory Insurance [Member]	Dec. 31, 2012 Inventory Insurance [Member]	Dec. 31, 2011 Inventory Insurance [Member]	Jan. 31, 2013 Subsequent Events [Member]	Mar. 31, 2013 Subsequent Events [Member]	Feb. 08, 2013 Subsequent Events [Member] 5 3/4% Senior Notes Due 2021 [Member]
Subsequent Event [Line Items]
Insurance proceeds received	$ 6.6	$ 19.7	$ 26.3				$ 3.7	$ 4.7	$ 3.4
Total settlement for the loss of inventory									11.8
Gain from insurance recoveries	2.8	14.6				3.5				8.3
Debt Intrument Face Amount				$ 330.0	$ 330.0						$ 500.0
Senior Notes				9.75%							5.75%
Period of maturity											Feb. 15, 2021