Shareholders' Equity (Preferred Shares) (Narrative) (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) item $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares
Class of Stock [Line Items]
Number of quarterly dividends in arrearage before preferred shareholders can elect additional board members | item	6
Number of additional board members the preferred shareholders can elect in the case of an excess arrearage of quarterly dividends | item	2
Affirmative vote of outstanding shares of a series of Preferred Shares required for any material and adverse amendment to the terms of series, percent	66.67%
Affirmative vote of outstanding shares of all Preferred Shares, voting as a single class, required to issue shares ranking senior to Preferred Shares, percent	66.67%
Redemption price per share | $ / shares	$ 25.00
Gross proceeds from issuance of preferred stock	$ 1,059,156	$ 561,177
EITF D-42 allocations	32,693	29,330
Series U, Series Y, Series Z and SeriesA Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, redemption amount	$ 1,050,000
Series H, Series I, Series J and Series K Preferred Stock [Member]
Class of Stock [Line Items]
Shares issued | shares	43,600,000
Preferred shares per depositary share | shares	0.001
Shares issued, price per share | $ / shares	$ 25.00
Gross proceeds from issuance of preferred stock	$ 1,090,000
Original issuance costs on preferred shares redeemed during the period	$ 30,800,000
Series S and Series T Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, redemption amount		$ 922,500
Series F and Series G Preferred Stock [Member]
Class of Stock [Line Items]
Shares issued | shares		23,200,000
Preferred shares per depositary share | shares		0.001
Shares issued, price per share | $ / shares		$ 25.00
Gross proceeds from issuance of preferred stock		$ 580,000
Original issuance costs on preferred shares redeemed during the period		$ 18,800