Public Offerings and Capital Stock - Additional Information (Detail)			3 Months Ended		25 Months Ended
	Apr. 01, 2016 USD ($)	Jan. 27, 2015 USD ($) $ / shares shares	Mar. 31, 2019 USD ($) $ / shares shares	Mar. 31, 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
Common Stock, issued			98,564,889			98,483,000
Common Stock, outstanding			98,564,889			98,483,000
Preferred stock, authorized			20,000,000
Number of shares authorized to repurchase under a share repurchase program								2,000,000
Number of common stock repurchased			0
Common stock remaining for issuance under the registration statement | $			$ 490,200,000
Registration statement declaration effective date			Apr. 13, 2016
Twenty Eighteen Dividend Reinvestment and Stock Purchase Plan
Capital Unit [Line Items]
Common Stock, authorized			15,303,119
Issuance of stock (in shares)			81,841
Stock issued, weighted average price per share | $ / shares			$ 4.36
Proceeds from issuance of common stock | $			$ 356,000
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 | $	$ 534,442,660
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
Number of share repurchase authorizations | item					6
FBR Sales Agreement
Capital Unit [Line Items]
Stock sales agreement value | $			$ 196,615,000
Stock sales agreement remaining amount | $			$ 152,100,000
Series A Preferred Stock
Capital Unit [Line Items]
Preferred stock, authorized			5,150,000
Preferred stock, par value | $ / shares			$ 0.01			$ 0.01
Preferred stock, liquidation preference | $ / shares			$ 25.00			$ 25.00
Preferred Stock, dividend rate			8.625%
Preferred stock redemption price | $ / shares			$ 25.00
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 | $ / shares			$ 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 | $ / shares			$ 0.01			$ 0.01
Preferred stock, liquidation preference | $ / shares			$ 25.00			$ 25.00
Preferred Stock, dividend rate			7.625%
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 | $ / shares		$ 24.50
Public offering net proceeds | $		$ 7,000,000
Proceeds on Preferred Stock issued | $				$ 525,000