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

Earnings per share - Additional Information (Detail)	3 Months Ended		9 Months Ended
Earnings per share - Additional Information (Detail)	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Options to purchase common stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding options not included in diluted earnings per share	636,900	787,440	688,636	2,600,874
Common stock equivalents [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding options not included in diluted earnings per share				331,775