Income per Common Share of the Trust - Options Exercised (Details) - shares	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2019	Sep. 30, 2019	Dec. 31, 2018
Stock Option \| Common shares
Stock Option Exercises [Line Items]
Amount of options exercised in period	251,000	374,000	151,000

Number of share options (or share units) exercised during the current period.

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Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration