Equity Incentive Plan (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended
	Jul. 31, 2015	Jul. 31, 2012	Mar. 31, 2016	Mar. 31, 2015
Equity Incentive Plan
Maximum number of common shares of beneficial interest available for issuance (in shares)			7,500,000
Summary of non-vested shares/units
Granted (in shares)			1,447
Weighted Average Grant Date Fair Value
Granted (in dollars per share)			$ 22.88
Other Disclosures
Share-based compensation expense			$ 33	$ 33
Restricted share awards
Summary of non-vested shares/units
Unvested at the beginning of the period (in shares)			540,885
Granted (in shares)			380,014
Vested (in shares)			(88,211)
Forfeited (in shares)			(263)
Unvested at the end of the period (in shares)			832,425
Weighted Average Grant Date Fair Value
Unvested at the beginning of the period (in dollars per share)			$ 26.73
Granted (in dollars per share)			19.61
Vested (in dollars per share)			23.39
Forfeited (in dollars per share)			30.91
Unvested at the end of the period (in dollars per share)			$ 23.83
Other Disclosures
Share-based compensation expense			$ 2,100	2,900
Total unrecognized compensation costs			$ 18,800
Weighted-average period of recognition of unrecognized share-based compensation expense			2 years 11 months 10 days
Total fair value of shares vested			$ 1,800
Performance Units
Summary of non-vested shares/units
Unvested at the end of the period (in shares)			419,467
Other Disclosures
Share-based compensation expense			$ 500	$ 1,100
Total unrecognized compensation costs			$ 600
Vesting period		4 years
Performance-based vesting period		3 years
Time-based vesting period		1 year
Restricted shares issued upon conversion of performance units (in shares)	838,934
Common shares available for future grant (in share)			3,742,666