Fair Value Measurements and Derivative Instruments (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Mar. 01, 2017
Fair Value Measurements And Derivative Instruments [Line Items]
Net gain (loss) on interest rate instruments	$ (536,000)	$ (991,000)	$ 248,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset (Liability) Transfers Between Levels	0	0	0
Impairment recovery, net	$ 0	$ 0	$ 93,000
Redemption Rights [Member] | Series E Preferred Stock [Member]
Fair Value Measurements And Derivative Instruments [Line Items]
Number of shares called by redemption				490,250
Level 3 [Member] | Redemption Rights [Member] | Series E Preferred Stock [Member]
Fair Value Measurements And Derivative Instruments [Line Items]
Assets fair value				$ 150,000