Preferred Stock (Schedule of Preferred Stock Activity) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Schedule of Preferred Stock Activity [Abstract]
Preferred stock, $0.01 par value, 10,000,000 shares authorized; 200,000 issued and outstanding as of June 30, 2018 and 250,000 issued and outstanding as of December 31, 2017	$ 172,858,000		$ 172,858,000		$ 214,262,000
Redemption of Preferred Stock			(42,897,000)
Accretion on preferred stock	$ (740,000)	$ 0	$ (1,493,000)	$ 0