Summary of Significant Accounting Policies Tax (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Summary Of Significant Accounting Policies [Abstract]
State and local income, franchise and excise tax (benefit)	$ 852	$ 963	$ 878
Alternative minimum tax credit (benefit)		(3,244)
Income and other tax expense (benefit)	$ 852	$ (2,281)	$ 878
Tax Treatment Of Dividends And Distributions Ordinary Dividends	$ 1.34739	$ 1.39604	$ 1.84454
Tax Treatment Of Dividends And Distributions Long Term Capital Gain	0.77923	0.61243	0.21423
Tax Treatment Of Dividends And Distributions Unrecaptured Section Twelve Hundred And Fifty Gain	0.24838	0.23403	0.06498
Dividends and distributions declared per Common Share outstanding	$ 2.37500	$ 2.24250	$ 2.12375