CONSOLIDATED STATEMENTS OF EQUITY - USD ($) shares in Thousands, $ in Thousands	Parent	Common Stock	Capital in Excess of Par Value	Cumulative Net Income	Cumulative Distributions	Non-controlling Interests	Total
Balance at beginning of period at Dec. 31, 2019	$ 776,943	$ 398	$ 867,346	$ 1,293,482	$ (1,384,283)	$ 8,483	$ 785,426
Balance (in shares) at Dec. 31, 2019		39,752
Equity activity
Common stock cash distributions	(22,581)				(22,581)		(22,581)
Vesting of performance-based stock units, including the payment of distributions	(586)				(586)		(586)
Vesting of performance-based stock units, including the payment of distributions (in shares)		82
Issuance of restricted stock		$ 1	(1)
Issuance of restricted stock (in shares)		76
Repurchase of common stock	(18,012)	$ (6)	(18,006)				(18,012)
Repurchase of common stock (in shares)		(616)
Stock-based compensation expense	1,777		1,777				1,777
Net income	63,633			63,633		89	63,722
Non-controlling interest distributions						(146)	(146)
Other	(3,545)	$ (1)	(3,544)				(3,545)
Other (in shares)		(76)
Balance at end of period at Mar. 31, 2020	797,629	$ 392	847,572	1,357,115	(1,407,450)	8,426	806,055
Balance (in shares) at Mar. 31, 2020		39,218
Balance at beginning of period at Dec. 31, 2019	776,943	$ 398	867,346	1,293,482	(1,384,283)	8,483	785,426
Balance (in shares) at Dec. 31, 2019		39,752
Equity activity
Net income							65,674
Balance at end of period at Jun. 30, 2020	778,894	$ 392	849,326	1,358,985	(1,429,809)	8,411	787,305
Balance (in shares) at Jun. 30, 2020		39,243
Balance at beginning of period at Mar. 31, 2020	797,629	$ 392	847,572	1,357,115	(1,407,450)	8,426	806,055
Balance (in shares) at Mar. 31, 2020		39,218
Equity activity
Common stock cash distributions	(22,359)				(22,359)		(22,359)
Issuance of restricted stock	(7)		(7)				(7)
Issuance of restricted stock (in shares)		25
Stock-based compensation expense	1,761		1,761				1,761
Net income	1,870			1,870		82	1,952
Non-controlling interest distributions						(97)	(97)
Balance at end of period at Jun. 30, 2020	778,894	$ 392	849,326	1,358,985	(1,429,809)	8,411	787,305
Balance (in shares) at Jun. 30, 2020		39,243
Equity activity
Common stock cash distributions	(22,368)				(22,368)		(22,368)
Stock-based compensation expense	1,693		1,693				1,693
Net income	12,217			12,217		121	12,338
Non-controlling interest distributions						(128)	(128)
Other	(19)		(19)				(19)
Other (in shares)		(1)
Balance at end of period at Sep. 30, 2020	770,417	$ 392	851,000	1,371,202	(1,452,177)	8,404	778,821
Balance (in shares) at Sep. 30, 2020		39,242
Equity activity
Common stock cash distributions	(22,368)				(22,368)		(22,368)
Issuance of restricted stock	(1)		(1)				(1)
Stock-based compensation expense	1,781		1,781				1,781
Net income	17,573			17,573		92	17,665
Non-controlling interest distributions						(92)	(92)
Balance at end of period at Dec. 31, 2020	767,402	$ 392	852,780	1,388,775	(1,474,545)	8,404	775,806
Balance (in shares) at Dec. 31, 2020		39,242
Equity activity
Common stock cash distributions	(22,405)				(22,405)		(22,405)
Vesting of performance-based stock units, including the payment of distributions	(764)	$ 1	(1)		(764)		(764)
Vesting of performance-based stock units, including the payment of distributions (in shares)		109
Stock-based compensation expense	1,852		1,852				1,852
Net income	13,762			13,762		88	13,850
Non-controlling interest distributions						(88)	(88)
Cash paid for taxes in lieu of common shares	(3,470)		(3,470)				(3,470)
Cash paid for taxes in lieu of common shares (in shares)		(84)
Other	(10)	$ 1	(11)				(10)
Other (in shares)		95
Balance at end of period at Mar. 31, 2021	756,367	$ 394	851,150	1,402,537	(1,497,714)	8,404	764,771
Balance (in shares) at Mar. 31, 2021		39,362
Balance at beginning of period at Dec. 31, 2020	767,402	$ 392	852,780	1,388,775	(1,474,545)	8,404	775,806
Balance (in shares) at Dec. 31, 2020		39,242
Equity activity
Net income							32,180
Balance at end of period at Jun. 30, 2021	753,976	$ 394	852,959	1,420,776	(1,520,153)	8,404	762,380
Balance (in shares) at Jun. 30, 2021		39,374
Balance at beginning of period at Mar. 31, 2021	756,367	$ 394	851,150	1,402,537	(1,497,714)	8,404	764,771
Balance (in shares) at Mar. 31, 2021		39,362
Equity activity
Common stock cash distributions	(22,439)				(22,439)		(22,439)
Stock-based compensation expense	1,958		1,958				1,958
Net income	18,239			18,239		91	18,330
Non-controlling interest distributions						(91)	(91)
Cash paid for taxes in lieu of common shares	(103)		(103)				(103)
Cash paid for taxes in lieu of common shares (in shares)		(3)
Other	(46)		(46)				(46)
Other (in shares)		15
Balance at end of period at Jun. 30, 2021	$ 753,976	$ 394	$ 852,959	$ 1,420,776	$ (1,520,153)	$ 8,404	$ 762,380
Balance (in shares) at Jun. 30, 2021		39,374