CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Condensed Consolidated Balance Sheets
Accounts receivable, trade, allowance (in dollars)	$ 828	$ 1,135
Common units, units issued	49,456,901	42,313,731
General partner units, interest (as a percent)	2.00%	2.00%
General partner units, equivalent units issued	1,003,227	858,583
General partner units, equivalent units outstanding	1,003,227	858,583
Treasury units, common units	47,420	43,630