Public Offerings and Capital Stock - Additional Information (Detail) (USD $)	3 Months Ended	9 Months Ended							3 Months Ended		0 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2014	May 22, 2014	Mar. 14, 2014	Dec. 31, 2013	Dec. 13, 2013	Oct. 03, 2011	Aug. 05, 2014 Anworth Mortgage Asset Corporation Twenty Fourteen Equity Compensation Plan	Sep. 30, 2014 Restricted Stock Units (RSUs)	Sep. 30, 2014 Twenty Twelve Dividend Reinvestment And Stock Purchase Plan	Apr. 05, 2013 Maximum	Mar. 14, 2012 Maximum Twenty Twelve Dividend Reinvestment And Stock Purchase Plan	Sep. 30, 2014 Series A Preferred Stock	Sep. 30, 2014 Series B Preferred Stock
Capital Unit [Line Items]
Common Stock, authorized	200,000,000	200,000,000			200,000,000							27,000,000
Common Stock, issued	118,554,025	118,554,025			138,717,000
Common Stock, outstanding	118,554,025	118,554,025			138,717,000
Preferred stock, authorized	20,000,000	20,000,000											5,150,000	3,150,000
Preferred stock, par value	$ 0.01	$ 0.01			$ 0.01
Preferred stock, liquidation preference	$ 25.00	$ 25.00			$ 25.00								$ 25.00	$ 25.00
Preferred Stock, dividend rate													8.625%	6.25%
Preferred stock, issued	1,919,000	1,919,000			1,919,000								1,919,378	1,009,640
Preferred stock, outstanding	1,919,000	1,919,000			1,919,000								1,919,378	1,009,640
Number of additional shares authorized to be repurchased			10,000,000	10,000,000		5,000,000
Number of common stock repurchased	6,819,372
Common stock repurchased, weighted average price	$ 5.10
Number of shares authorized to repurchase under a share repurchase program							2,000,000
Issuance of common stock (in shares)									10,000	75,783
Common stock issued, weighted average price per share										$ 5.18
Proceeds from issuance of common stock										$ 393,000
Remaining number of shares to be issued										16,560,000
Common stock, public offering											544,727,778
Common stock remaining for issuance under the registration statement		$ 544,700,000
Shelf registration statement expiration date		April 8, 2013
Maximum authorized shares of common stock under grant of stock options and other stock-based awards								2,000,000