Public Offerings and Capital Stock - Additional Information (Detail)			3 Months Ended	9 Months Ended		25 Months Ended
	Apr. 04, 2019 USD ($)	Jan. 27, 2015 USD ($) $ / shares shares	Sep. 30, 2019 USD ($) $ / shares shares	Sep. 30, 2019 USD ($) $ / shares shares	Sep. 30, 2018 USD ($)	Jan. 22, 2016 item	Dec. 31, 2018 $ / shares shares	Aug. 05, 2014 shares	Oct. 03, 2011 shares
Capital Unit [Line Items]
Common Stock, authorized			200,000,000	200,000,000			200,000,000
Common Stock, issued			98,767,675	98,767,675			98,483,000
Common Stock, outstanding			98,767,675	98,767,675			98,483,000
Preferred stock, authorized			20,000,000	20,000,000
Number of shares authorized to repurchase under a share repurchase program									2,000,000
Number of common stock repurchased				0
Maximum amount of capital stock that may be offered per a registration statement | $	$ 490,236,182
Capital stock available for future issuance | $			$ 490,200,000	$ 490,200,000
Twenty Eighteen Dividend Reinvestment and Stock Purchase Plan
Capital Unit [Line Items]
Common Stock, authorized			15,303,119	15,303,119
Issuance of stock (in shares)			84,755
Stock issued, weighted average price per share | $ / shares			$ 3.81
Proceeds from issuance of common stock | $			$ 322,600
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
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	45,000,000
Number of share repurchase authorizations | item						6
FBR Sales Agreement
Capital Unit [Line Items]
Stock sales agreement value | $			$ 196,615,000	$ 196,615,000
Stock sales agreement remaining amount | $			$ 152,100,000	$ 152,100,000
Series A Preferred Stock
Capital Unit [Line Items]
Preferred stock, authorized			5,150,000	5,150,000
Preferred stock, par value | $ / shares			$ 0.01	$ 0.01			$ 0.01
Preferred stock, liquidation preference | $ / shares			25.00	$ 25.00			$ 25.00
Preferred Stock, dividend rate				8.625%
Preferred stock redemption price | $ / shares			$ 25.00	$ 25.00
Preferred stock, issued			1,919,378	1,919,378			1,919,000
Preferred stock, outstanding			1,919,378	1,919,378			1,919,000
Series B Preferred Stock
Capital Unit [Line Items]
Preferred stock, authorized			3,150,000	3,150,000
Preferred stock, liquidation preference | $ / shares			$ 25.00	$ 25.00
Preferred Stock, dividend rate				6.25%
Preferred stock, issued			779,743	779,743
Preferred stock, outstanding			779,743	779,743
Series C Preferred Stock
Capital Unit [Line Items]
Preferred stock, authorized			5,000,000	5,000,000
Preferred stock, par value | $ / shares			$ 0.01	$ 0.01			$ 0.01
Preferred stock, liquidation preference | $ / shares			$ 25.00	$ 25.00			$ 25.00
Preferred Stock, dividend rate				7.625%
Preferred stock, issued			2,010,278	2,010,278			2,010,000
Preferred stock, outstanding			2,010,278	2,010,278			2,010,000
Issuance of stock (in shares)		300,000
Preferred stock, par value | $ / shares		$ 24.50
Public offering net proceeds | $		$ 7,000,000
Proceeds on Preferred Stock issued | $				$ (318,000)	$ 525,000