Stockholder's Equity (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Feb. 28, 2019
Preferred Stock [Line Items]
Preferred stock redemption charge	$ 0	$ 0	$ 9,769,000
Series I Preferred Stock
Preferred Stock [Line Items]
Equivalent number of common stock on conversion of preferred shares (in shares)	0.8857
Series J Preferred Stock
Preferred Stock [Line Items]
Preferred stock redemption charge			$ 9,769,000
Equity Shelf Program
Preferred Stock [Line Items]
Aggregate amount of common stock offered to sell				$ 1,500,000,000
Remaining capacity	$ 1,075,537,000
Stock options
Preferred Stock [Line Items]
Number of shares not included in the computation of diluted earnings per share because such options were anti-dilutive	4,935,804