Equity - Additional Information (Details) - USD ($)	1 Months Ended		12 Months Ended
	Jul. 31, 2015	Jul. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Equity [Line Items]
Common shares issued through public offering and direct share purchase plan during period (in shares)			577,823	2,266,191	2,600,795
Proceeds from issuance of common shares			$ 12,186,000	$ 19,382,000	$ 23,563,000
Shares issued, net of forfeitures (in shares)			1,084,835	860,730	37,678
OP unit equivalent in common shares (in unit per share)			1.13
OP units, redemptions			$ 0	$ 0	$ 1,962,000
Shares issued for units redeemed (in shares)			48,549	32,780	29,086
Partners' capital account, exchanges and conversions			$ 210,000	$ 165,000	$ 148,000
OP units outstanding (in units)			3,350,000
Payments to acquire interest in joint venture			$ 0	$ 4,022,000	$ 2,100,000
Joint Venture [Member] | Philadelphia, Pennsylvania [Member] | Office Building [Member]
Equity [Line Items]
Payments to acquire interest in joint venture	$ 4,022,000	$ 2,100,000
Real state, ownership percentage	100.00%
Former LCIF II Partners [Member]
Equity [Line Items]
OP units redeemed (in units)					170,193
OP units, redemptions					$ 1,962,000
Common Stock [Member]
Equity [Line Items]
Number of shares authorized to be repurchased (in shares)	10,000,000
Repurchase of common shares (in shares)			1,184,113	2,216,799
Average cost per share (usd per share)			$ 7.56	$ 8.29
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Equity [Line Items]
Effect net of tax			$ (1,033,000)	$ (1,939,000)
Series C [Member]
Equity [Line Items]
Preferred shares outstanding (in shares)			1,935,400	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	$ 20,797,000	$ 25,813,000
At The Market [Member]
Equity [Line Items]
Common shares issued through public offering and direct share purchase plan during period (in shares)			976,109	0	0
Value authorized			$ 125,000,000
Value, new issues			$ 10,498,000