Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Current assets:
Trade accounts receivable, allowances for doubtful accounts	$ 297	$ 235
Other assets:
Patents, trademarks, and other intangible assets, accumulated amortization	$ 669	$ 592
Partners' capital:
Common units issued and outstanding	9,163,738	9,163,738
Subordinated units issued and outstanding	6,273,970	6,273,970