Equity - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jul. 31, 2015
Equity [Line Items]
Common shares issued through public offering and direct share purchase plan during period (in shares)	0	0	577,823
Proceeds from issuance of common shares	$ (2,818,000)	$ 16,804,000	$ 12,186,000
Preferred shares outstanding (in shares)	1,935,400	1,935,400
Shares issued, net of forfeitures (in shares)	965,932	835,234	1,084,835
Unsettled repurchases	$ 2,641,000
OP unit equivalent in common shares (in unit per share)	1.13
Shares issued for units redeemed (in shares)	53,388	140,746	48,549
Partners' capital account, exchanges and conversions	$ 189,000	$ 584,000	$ 210,000
OP units outstanding (in units)	3,177,000
Common Shares [Member]
Equity [Line Items]
Number of shares authorized to be repurchased (in shares)	10,000,000			10,000,000
Repurchase of common shares (in shares)	5,851,252	0	1,184,113
Average cost per share (usd per share)	$ 8.05		$ 7.56
Series C [Member]
Equity [Line Items]
Preferred shares outstanding (in shares)	1,935,400
Dividend rate (usd per share)	$ 3.25
Preferred shares, liquidation preference	$ 96,770,000
Preferred shares to common shares conversion ratio	2.4339
Series C [Member] | Minimum [Member]
Equity [Line Items]
Common share closing price percent of conversion price	125.00%
Public Offering And Direct Share Purchase Plan Proceeds [Member]
Equity [Line Items]
Proceeds from issuance of common shares			$ 4,115,000
At The Market [Member]
Equity [Line Items]
Common shares issued through public offering and direct share purchase plan during period (in shares)	0	1,593,603	976,109
Value authorized	$ 125,000,000
Value, new issues		$ 17,362,000	$ 10,498,000