Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Net number of share options (or share units) granted during the period.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Shareholders' Equity / Partners' Capital - 2012 Equity Incentive Plan Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Stock options and Restricted stock units
Class of Stock [Line Items]
Allocated share-based compensation expense	$ 0.8	$ 1.1	$ 2.7	$ 3.2
Stock options and Restricted stock units \| General and Administrative Expense
Class of Stock [Line Items]
Allocated share-based compensation expense	0.5	0.7	1.6	1.9
Stock options and Restricted stock units \| Property Management Expense
Class of Stock [Line Items]
Allocated share-based compensation expense	$ 0.3	$ 0.4	$ 1.1	$ 1.3
Restricted stock units
Class of Stock [Line Items]
Restricted stock unit grants in period (in shares)			304,400	174,000
2012 Equity Incentive Plan \| Stock options and Restricted stock units
Class of Stock [Line Items]
Vesting period for stock options and restricted stock units			4 years
2012 Equity Incentive Plan \| Stock options
Class of Stock [Line Items]
Granted (in shares)			140,000	385,600
Expiration period for stock options			10 years