Consolidated Balance Sheets (Parentheticals) (USD $)
In Thousands, except Share data, unless otherwise specified
Dec. 31, 2012
Dec. 31, 2011
Statement of Financial Position [Abstract]    
Allowance for doubtful accounts $ 2,264 $ 2,286
Common units issued (in shares) 30,786,100 25,183,039
Common units outstanding (in shares) 30,786,100 25,183,039
Common units held in treasury (in shares) 4,154,371 2,808,725
Common units held in treasury, at cost $ 63,181 $ 48,099