Public Offerings and Capital Stock - Additional Information (Detail) - USD ($)			3 Months Ended	6 Months Ended
	Apr. 01, 2016	Jan. 27, 2015	Jun. 30, 2017	Jun. 30, 2017	Dec. 31, 2016	Mar. 31, 2015	Aug. 05, 2014	Oct. 03, 2011
Capital Unit [Line Items]
Common Stock, authorized			200,000,000	200,000,000	200,000,000
Common Stock, issued			97,497,875	97,497,875	95,718,000
Common Stock, outstanding			97,497,875	97,497,875	95,718,000
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
Common stock remaining for issuance under the registration statement				$ 506,200,000
Registration statement declaration effective date				Apr. 13, 2016
Twenty Fifteen Dividend Reinvestment And Stock Purchase Plan
Capital Unit [Line Items]
Issuance of stock (in shares)				52,686
Common stock issued, weighted average price per share				$ 5.88
Proceeds from issuance of common stock				$ 310,000
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
Maximum | Twenty Fifteen Dividend Reinvestment And Stock Purchase Plan
Capital Unit [Line Items]
Common Stock, authorized						16,397,203
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
FBR Sales Agreement
Capital Unit [Line Items]
Stock sales agreement value			$ 196,615,000	$ 196,615,000
Stock sales agreement remaining amount			$ 168,300,000	$ 168,300,000
Series A Preferred Stock
Capital Unit [Line Items]
Preferred stock, authorized			5,150,000	5,150,000
Preferred stock, par value			$ 0.01	$ 0.01	$ 0.01
Preferred stock, liquidation preference			25.00	$ 25.00	$ 25.00
Preferred Stock, dividend rate				8.625%
Preferred stock redemption price			$ 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			$ 25.00	$ 25.00
Preferred Stock, dividend rate				6.25%
Preferred stock, issued			625,295	625,295
Preferred stock, outstanding			625,295	625,295
Series C Preferred Stock
Capital Unit [Line Items]
Preferred stock, authorized			5,000,000	5,000,000
Preferred stock, par value			$ 0.01	$ 0.01	$ 0.01
Preferred stock, liquidation preference			$ 25.00	$ 25.00	$ 25.00
Preferred Stock, dividend rate				7.625%
Preferred stock, issued			1,580,006	1,580,006	486,000
Preferred stock, outstanding			1,580,006	1,580,006	486,000
Issuance of stock (in shares)		300,000
Preferred stock, par value		$ 24.50
Public offering net proceeds		$ 7,000,000
Proceeds on Series C Preferred Stock issued			$ (22,065,000)	$ (26,920,000)
Series C Preferred Stock | FBR Sales Agreement
Capital Unit [Line Items]
Issuance of stock (in shares)				896,645
Proceeds on Series C Preferred Stock issued				$ 22,100,000