Shareholders' Equity / Partners' Capital - 2012 Equity Incentive Plan Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Stock options and Restricted stock units
Class of Stock [Line Items]
Allocated share-based compensation expense	$ 1.1	$ 0.9	$ 3.2	$ 2.7
Stock options and Restricted stock units | General and Administrative Expense
Class of Stock [Line Items]
Allocated share-based compensation expense	0.7	0.5	1.9	1.6
Stock options and Restricted stock units | Property Management Expense
Class of Stock [Line Items]
Allocated share-based compensation expense	$ 0.4	$ 0.4	$ 1.3	$ 1.1
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
Expiration period for stock options and restricted stock units			10 years
2012 Equity Incentive Plan | Stock options
Class of Stock [Line Items]
Granted (in shares)			385,600	708,000
2012 Equity Incentive Plan | Restricted stock units
Class of Stock [Line Items]
Restricted stock unit grants in period (in shares)			174,000	74,100