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Equity Incentive Plan - Additional Information (Details) $ / shares in Units, $ in Millions					1 Months Ended			12 Months Ended
	Jan. 16, 2019 shares	Mar. 01, 2018 $ / shares shares	Jun. 01, 2015 shares	May 17, 2013 shares	Jan. 31, 2018 shares	Jan. 31, 2017 shares	Jan. 31, 2016 shares	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) shares
Independent Trustees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Trustee fees | $								$ 0.1	$ 0.1	$ 0.1
Common shares issued as compensation for services performed (in shares)					21,670	23,980	26,488
Independent Trustees | Subsequent Event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares issued as compensation for services performed (in shares)	27,870
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Trustee fees paid in shares (up to 100%) (at least 50%) (in percentage)								50.00%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Trustee fees paid in shares (up to 100%) (at least 50%) (in percentage)								100.00%
2018 Time-Based LTIP Unit Award
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Granted (in shares)		97,968
Shares granted (in shares)		97,968
Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized (in shares)				3,000,000
Equity Incentive Plan | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period for share awards under equity				3 years
Equity Incentive Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period for share awards under equity				5 years
2010 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares available for issuance (in shares)								1,400,529
Number of trading days preceding the reporting date for which average of closing price of common shares is taken								10 days
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Granted (in shares)								5,000	5,000	0
Unrecognized compensation costs | $								$ 0.1	$ 0.1
Weighted - average period for recognition of unrecognized compensation costs								2 years 4 months 24 days
Compensation expense recognized | $								$ 0.1	$ 0.8	$ 1.3
Shares granted (in shares)								5,000	5,000	0
Shares forfeited (in shares)								24,096	25,870	0
Long Term Incentive Plan Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Granted (in shares)			183,300					244,917	223,922	112,251
Weighted - average period for recognition of unrecognized compensation costs								1 year 9 months 18 days
Compensation expense recognized | $								$ 3.6	$ 2.5	$ 1.2
Exchange ratio								1
Shares granted (in shares)			183,300					244,917	223,922	112,251
Shares forfeited (in shares)								183,300	0	0
Percent of units with full parity that have vested								100.00%
Total unrecognized compensation cost related to LTIP Units | $								$ 5.0	$ 4.4
Long Term Incentive Plan Units | Awarded June 1, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Granted (in shares)			183,300
Shares granted (in shares)			183,300
2018 Performance-Based LTIP Unit Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Granted (in shares)		146,949
Shares granted (in shares)		146,949
Grants in period, intrinsic value, amount (in dollars per share) | $ / shares		$ 17.02
2018 Performance-Based LTIP Unit Awards | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of target value to be paid out								50.00%
2018 Performance-Based LTIP Unit Awards | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of target value to be paid out								150.00%

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- Definition

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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Unrecognized cost of unvested share-based compensation awards.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, 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 equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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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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Per share weighted average intrinsic value of equity-based compensation awards granted. Excludes stock and unit options.

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The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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Number of shares (or other type of equity) issued during the period as a result of any equity-based compensation plan other than an employee stock ownership plan (ESOP), net of any shares forfeited. Shares issued could result from the issuance of restricted stock, the exercise of stock options, stock issued under employee stock purchase plans, and/or other employee benefit plans.

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Fees charged annually for the professional services of a trustee, usually quoted as a percentage of the funds being managed. The fee for appointing an offshore Trustee is included in the trust price.

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Number of trading days preceding the reporting date for which average of closing price of common shares is taken.

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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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Unrecognized compensation cost related to long term incentive plan units.

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