Commitment and Contingencies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended			12 Months Ended
	Nov. 30, 2010 T	May 31, 2010 Y	Oct. 21, 2009 Y	Dec. 31, 2012 acre	Dec. 31, 2011	Dec. 31, 2010
Commitments and Contingencies Disclosure [Line Items]
Total rent expense				$ 0.1	$ 2.1	$ 2.0
Purchase obligation				6.7
Purchase obligation due in 2013				4.5
Purchase obligation due in 2014				0.3
Purchase obligation due in 2015				1.2
Purchase obligation due in 2016				0.7
Area of land contributed for joint venture				57
Market value of land contributed for joint venture				6.0
Estimated contribution for joint venture				9.9
Amount funded for joint venture				0.9
Unencumbered and unrestricted cash or cash equivalents				25
Required net worth excluding deferred revenue for construction loan covenant				350
Principal repayment guaranteed				33.00%
Dispute settlement					9.0
Aggregate environmental-related accruals				1.6	1.5
Threshold of ownership percentage in Company for private investigation of compliance				5.00%
Other income related to contract termination				0.8
Strategic alliance agreement reimbursement period, in years			3
Extension to strategic alliance agreement reimbursement period, in years		3
Product amount to be sold or delivered, in tons	3,900,000
Surety bonds | Certain development projects
Commitments and Contingencies Disclosure [Line Items]
Commitment obligations				10.3	15.7
Surety bonds | Standby letters of credit
Commitments and Contingencies Disclosure [Line Items]
Commitment obligations				$ 1.1	$ 0.8