Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income Tax Disclosure [Abstract]
Statutory federal income tax rate	35.00%	35.00%	35.00%	35.00%
State taxes, net of credits	(0.30%)	1.50%	(0.30%)	1.50%
Change in valuation allowances	2.60%	3.50%	2.60%	3.50%
Federal manufacturing deduction	(1.40%)	0.00%	(1.40%)	0.00%
Settlement of Uncertian Tax Positions	(0.80%)	(57.30%)	(0.20%)	(41.60%)
Increase in uncertain tax position	1.90%	0.00%	0.50%	0.00%
Interest accrued on uncertain tax positions	0.20%	8.40%	0.10%	13.90%
Conversion From Alternative Fuel Mixture Tax Credit to Cellulosic Biofuel Producer Tax Credit	0.00%	0.20%	0.00%	(36.80%)
Effective Income Tax Rate Reconciliation, Tax Credit, Cellulosic Biofuel Producer Credit, Percent	0.00%	(43.00%)	0.00%	(81.50%)
Other Federal Credits	0.50%	0.00%	(0.80%)	0.00%
State rate adjustments	(0.50%)	(10.50%)	2.30%	(8.10%)
Effective Income Tax Rate Reconciliation, Prior Year Income Taxes, Percent	(0.10%)	(0.50%)	3.20%	(3.90%)
Other	0.30%	(1.00%)	(0.10%)	2.80%
Effective tax rate	37.40%	(63.70%)	40.90%	(115.20%)
Estimated Annual Effective Tax Rate	35.00%	39.00%
Excess Tax Benefit from Share-based Compensation			$ 1.5
Unrecognized excess tax benefits	0.8		0.8
Deferred Tax Assets, State Taxes	2.9		2.9
Deferred Tax Assets, Other	$ 1.5		$ 1.5