Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Deferred tax assets
Allowance for doubtful accounts	$ 696	$ 872
Asset impairment	764	756
Inventory	2,792	1,724
Deferred compensation	3,660	4,096
Other accrued liabilities	5,772	5,474
Hedging	700	1,033
Net operating loss carryforwards	310	392
Other	3,001	1,069
Total deferred tax assets	17,695	15,416
Less valuation allowance on deferred tax assets	(273)	(344)
Net deferred tax assets	17,422	15,072
Deferred tax liabilities
Property, plant and equipment	30,235	28,766
Prepaid and other insurance reserves	3,855	2,504
Investment in unconsolidated affiliate	433	640
Other	695	713
Total deferred tax liabilities	35,218	32,623
Net deferred tax liabilities	(17,796)	(17,551)
Consolidated balance sheet classification:
Net current deferred tax assets	3,224	4,275
Net noncurrent deferred tax liabilities	(21,020)	(21,826)
Net deferred tax liabilities	(17,796)	(17,551)
Net deferred tax liabilities by tax jurisdiction:
Federal	(16,324)	(15,724)
State	(1,472)	(1,827)
Net deferred tax liabilities	$ (17,796)	$ (17,551)