Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Current assets:
Trade accounts receivable, allowances for doubtful accounts	$ 235	$ 304
Other assets:
Patents, trademarks, and other intangible assets, accumulated amortization	$ 469	$ 566
Partners' equity:
Common units issued and outstanding	9,101,308
Subordinated units issued and outstanding	6,273,970