Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2011	Dec. 31, 2010
Current assets:
Allowance for accounts receivable, trade	$ 1,004	$ 1,232
Limited partner units:
Common stock, shares issued	32,541,390	27,363,451
Subordinated shares, shares issued	4,743,750	4,743,750
Subordinated shares, shares outstanding	4,743,750	4,743,750
General partners, interest	2.00%	2.00%
General partners, shares issued	757,722	653,318
General partners, shares outstanding	757,722	653,318
Treasury units	25,601	15,756