Schedule of Accounts Receivable (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Trade customers	$ 409,998	$ 391,401
Affiliates	123	122
Allowance for doubtful accounts	(10,851)	(10,969)
Receivables from trade customers and affiliates, net	399,270	380,554
Federal and state taxes	3,335	16,113
Other	15,395	10,705
Accounts receivable, net	$ 418,000	$ 407,372