Accounts Receivable (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Accounts Receivable, Net [Abstract]
Trade customers	$ 404,678	$ 388,949
Affiliates	333	258
Allowance for doubtful accounts	(9,832)	(11,172)
Receivables from trade customers and affiliates, net	395,179	378,035
Federal and state taxes	20,421	4,011
Other	17,425	18,113
Accounts receivable, net	$ 433,025	$ 400,159