CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION (Unaudited) (Parenthetical) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Cash pledged as collateral	$ 1,042,671	$ 579,213
Credit risk transfer securities, pledged assets	417,403	363,944
Residential mortgage loans, pledged assets	1,608,935	1,169,496
Mortgage servicing rights, pledged assets	4,164	5,224
Commercial real estate debt investments, pledged assets	2,733,405	3,070,993
Commercial real estate debt and preferred equity, held for investment, pledged assets	652,897	520,329
Corporate debt, pledged assets	$ 642,016	$ 600,049
Common Stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common Stock, shares authorized (in shares)	1,909,750,000	1,929,300,000
Common Stock, shares issued (in shares)	1,164,333,831	1,159,585,078
Common Stock, shares outstanding (in shares)	1,164,333,831	1,159,585,078
7.625% Series C Cumulative Redeemable Preferred Stock
Preferred Stock dividend rate, percentage	7.625%	7.625%
Cumulative redeemable preferred stock, shares authorized (in shares)	12,000,000	12,000,000
Cumulative redeemable preferred stock, shares issued (in shares)	7,000,000	12,000,000
Cumulative redeemable preferred stock, shares outstanding (in shares)	7,000,000	12,000,000
7.50% Series D Cumulative Redeemable Preferred Stock
Preferred Stock dividend rate, percentage	7.50%	7.50%
Cumulative redeemable preferred stock, shares authorized (in shares)	18,400,000	18,400,000
Cumulative redeemable preferred stock, shares issued (in shares)	18,400,000	18,400,000
Cumulative redeemable preferred stock, shares outstanding (in shares)	18,400,000	18,400,000
7.625% Series E Cumulative Redeemable Preferred Stock
Preferred Stock dividend rate, percentage	7.625%	7.625%
Cumulative redeemable preferred stock, shares authorized (in shares)	11,500,000	11,500,000
Cumulative redeemable preferred stock, shares issued (in shares)	0	11,500,000
Cumulative redeemable preferred stock, shares outstanding (in shares)	0	11,500,000
6.95% Series F Cumulative Redeemable Preferred Stock
Preferred Stock dividend rate, percentage	6.95%	6.95%
Cumulative redeemable preferred stock, shares authorized (in shares)	28,800,000	28,800,000
Cumulative redeemable preferred stock, shares issued (in shares)	28,800,000	28,800,000
Cumulative redeemable preferred stock, shares outstanding (in shares)	28,800,000	28,800,000
6.50% Series G Cumulative Redeemable Preferred Stock
Preferred Stock dividend rate, percentage	6.50%	6.50%
Cumulative redeemable preferred stock, shares authorized (in shares)	19,550,000	0
Cumulative redeemable preferred stock, shares issued (in shares)	17,000,000	0
Cumulative redeemable preferred stock, shares outstanding (in shares)	17,000,000	0
Non-Agency Mortgage-backed Securities
Mortgage-backed securities, pledged assets	$ 435,877	$ 516,078
Agency Mortgage-Backed Securities
Mortgage-backed securities, pledged assets	$ 80,997,975	$ 83,628,132