Condensed Consolidated Statements of Changes in Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common stock	Capital in excess of par value	Cumulative net income	Cumulative dividends	Accumulated other comprehensive income/(loss)
Balance at Dec. 31, 2017	$ 210,561	$ 137	$ 265,335	$ 618,120	$ (673,175)	$ 144
Balance, Shares at Dec. 31, 2017		13,735
Shares of Beneficial Interest:
Issued, net	68		68
Issued, net (in shares)		11
Restricted stock-based compensation expense	413		413
Dividends ($2.035/share) for nine months ended September 30, 2019, ($.68/share) for three months ended September 30, 2019, ($2.005/share) for nine months ended September 30, 2018 and ($.67/share) for three months ended September 30, 2018	(27,552)				(27,552)
Comprehensive income:
Net income	19,783			19,783
Unrealized derivative gain/(loss) on cash flow hedges	81
Unrealized gain/(loss) on interest rate cap	82					82
Subtotal - comprehensive income	19,865			19,783		82
Balance at Sep. 30, 2018	203,355	$ 137	265,816	637,903	(700,727)	226
Balance, Shares at Sep. 30, 2018		13,746
Balance at Jun. 30, 2018	207,990	$ 137	265,544	633,529	(691,518)	298
Balance, Shares at Jun. 30, 2018		13,744
Shares of Beneficial Interest:
Issued, net	113		113
Issued, net (in shares)		2
Restricted stock-based compensation expense	159		159
Dividends ($2.035/share) for nine months ended September 30, 2019, ($.68/share) for three months ended September 30, 2019, ($2.005/share) for nine months ended September 30, 2018 and ($.67/share) for three months ended September 30, 2018	(9,209)				(9,209)
Comprehensive income:
Net income	4,374			4,374
Unrealized derivative gain/(loss) on cash flow hedges	(73)
Unrealized gain/(loss) on interest rate cap	(72)					(72)
Subtotal - comprehensive income	4,302			4,374		(72)
Balance at Sep. 30, 2018	203,355	$ 137	265,816	637,903	(700,727)	226
Balance, Shares at Sep. 30, 2018		13,746
Balance at Dec. 31, 2018	198,610	$ 137	266,031	642,316	(710,006)	132
Balance, Shares at Dec. 31, 2018		13,747
Shares of Beneficial Interest:
Issued, net	(56)	$ 1	(57)
Issued, net (in shares)		10
Restricted stock-based compensation expense	504		504
Dividends ($2.035/share) for nine months ended September 30, 2019, ($.68/share) for three months ended September 30, 2019, ($2.005/share) for nine months ended September 30, 2018 and ($.67/share) for three months ended September 30, 2018	(27,988)				(27,988)
Comprehensive income:
Net income	13,126			13,126
Unrealized derivative gain/(loss) on cash flow hedges	429					429
Subtotal - comprehensive income	13,555			13,126		429
Balance at Sep. 30, 2019	184,625	$ 138	266,478	655,442	(737,994)	561
Balance, Shares at Sep. 30, 2019		13,757
Balance at Jun. 30, 2019	188,540	$ 138	266,252	650,789	(728,639)
Balance, Shares at Jun. 30, 2019		13,757
Shares of Beneficial Interest:
Issued, net	53		53
Restricted stock-based compensation expense	173		173
Dividends ($2.035/share) for nine months ended September 30, 2019, ($.68/share) for three months ended September 30, 2019, ($2.005/share) for nine months ended September 30, 2018 and ($.67/share) for three months ended September 30, 2018	(9,355)				(9,355)
Comprehensive income:
Net income	4,653			4,653
Unrealized derivative gain/(loss) on cash flow hedges	561					561
Subtotal - comprehensive income	5,214			4,653		561
Balance at Sep. 30, 2019	$ 184,625	$ 138	$ 266,478	$ 655,442	$ (737,994)	$ 561
Balance, Shares at Sep. 30, 2019		13,757