Condensed Consolidated Statement of Equity (Unaudited) Statement - 3 months ended Mar. 31, 2018 - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Cumulative Net Income	Cumulative Dividends
Beginning balance at Dec. 31, 2017	$ 1,789,883	$ 1,251	$ 3,173,429	$ (1,299)	$ 1,018,348	$ (2,401,846)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock	239		239
Common stock redemptions	(680)		(680)
Share-based compensation	2,822	1	2,821
Net income	9,180				9,180
Reclassification adjustments for losses included in net income (interest expense)	147			147
Gains arising during the period on interest rate swaps	513			513
Dividends to common stockholders ($0.30 per share)	(37,556)					(37,556)
Ending balance at Mar. 31, 2018	$ 1,764,548	$ 1,252	$ 3,175,809	$ (639)	$ 1,027,528	$ (2,439,402)