Public Offerings and Capital Stock - Additional Information (Detail) - USD ($)			12 Months Ended
	Apr. 01, 2016	Jan. 27, 2015	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2015	Aug. 05, 2014	Oct. 03, 2011
Capital Unit [Line Items]
Common Stock, authorized			200,000,000	200,000,000
Common Stock, issued			98,849,383	98,483,000
Common Stock, outstanding			98,849,383	98,483,000
Preferred stock, authorized			20,000,000
Number of shares authorized to repurchase under a share repurchase program								2,000,000
Common stock remaining for issuance under the registration statement			$ 490,200,000
Registration statement declaration effective date			Apr. 19, 2019
Twenty Fifteen Dividend Reinvestment And Stock Purchase Plan
Capital Unit [Line Items]
Issuance of stock (in shares)			346,335
Stock issued, weighted average price per share			$ 3.92
Proceeds from issuance of common stock			$ 1,360,000
Anworth Mortgage Asset Corporation 2014 Equity Compensation Plan
Capital Unit [Line Items]
Maximum authorized shares of common stock under grant of stock options and other stock-based awards							2,000,000
Maximum
Capital Unit [Line Items]
Common stock, public offering	$ 490,236,182
Maximum | Twenty Fifteen Dividend Reinvestment And Stock Purchase Plan
Capital Unit [Line Items]
Common Stock, outstanding						15,303,119
Through Six Separate Authorizations Between December 13, 2013 and January 22, 2016
Capital Unit [Line Items]
Number of additional shares authorized to be repurchased			45,000,000
FBR Sales Agreement
Capital Unit [Line Items]
Stock sales agreement remaining amount			$ 152,700,000
FBR Sales Agreement | Maximum
Capital Unit [Line Items]
Stock sales agreement value			$ 196,615,000
Series A Preferred Stock
Capital Unit [Line Items]
Preferred stock, authorized			5,150,000
Preferred stock, par value			$ 0.01	$ 0.01
Preferred stock, liquidation preference			$ 25.00	$ 25.00
Preferred Stock, dividend rate			8.625%
Preferred stock, issued			1,919,378	1,919,000
Preferred stock, outstanding			1,919,378	1,919,000
Series B Preferred Stock
Capital Unit [Line Items]
Preferred stock, authorized			3,150,000
Preferred stock, liquidation preference			$ 25.00
Preferred Stock, dividend rate			6.25%
Preferred stock, issued			779,743
Preferred stock, outstanding			779,743
Series C Preferred Stock
Capital Unit [Line Items]
Preferred stock, authorized			5,000,000
Preferred stock, par value			$ 0.01	$ 0.01
Preferred stock, liquidation preference			$ 25.00	$ 25.00
Preferred Stock, dividend rate			7.625%
Preferred stock redemption price			$ 25.00
Preferred stock, issued			2,010,278	2,010,000
Preferred stock, outstanding			2,010,278	2,010,000
Issuance of stock (in shares)		300,000
Preferred stock, par value		$ 24.50
Public offering net proceeds		$ 7,000,000
Proceeds on Preferred Stock issued			$ (318,000)	$ 525,000	$ 42,312,000