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 - Summary of Earnings Per Share (Parenthetical) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Warrants expire date	2013-04-13
Number of antidilutive warrants, options and restricted shares, for the year	1,936,871	1,142,028	1,254,279
CIBC World Markets Corp. [Member]
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Acquisition date of CIBC World Markets Corp.	Jan. 14, 2008
Warrants expire date	2013-04-13
Class A Stock [Member] \| CIBC World Markets Corp. [Member]
Schedule Of Earnings Per Share Basic And Diluted [Line Items]
Company issued a warrant to purchase share of Class A Stock	1,000,000
Class A Stock exercisable	48.62
Period for exercise of warrant	5 years