Earnings (loss) per share (Narrative) (Details)	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Incremental Common Shares Attributable to Share-based Payment Arrangements	372,000	339,000
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	335,000	668,000

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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+ Details