Public Offerings and Capital Stock - Additional Information (Detail) (USD $)	3 Months Ended			9 Months Ended				3 Months Ended	9 Months Ended				9 Months Ended	1 Months Ended		9 Months Ended			9 Months Ended
	Sep. 30, 2013	Mar. 31, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Oct. 03, 2011	Sep. 30, 2013 Dividend Reinvestment and Stock Purchase 2012 Plan	Sep. 30, 2013 Dividend Reinvestment and Stock Purchase 2012 Plan	Sep. 30, 2013 Anworth Mortgage Asset Corporation 2004 Equity Compensation Plan	Dec. 31, 2005 Anworth Mortgage Asset Corporation 2004 Equity Compensation Plan	Nov. 07, 2005 Anworth Mortgage Asset Corporation 2004 Equity Compensation Plan	Sep. 30, 2013 Previously Reported Dividend Reinvestment and Stock Purchase 2012 Plan	Apr. 05, 2013 Maximum	Mar. 14, 2012 Maximum Dividend Reinvestment and Stock Purchase 2012 Plan	Sep. 30, 2013 Series A Preferred Stock	Sep. 30, 2013 Series A Preferred Stock Controlled Equity Offering Sales Agreement	May 27, 2011 Series A Preferred Stock Controlled Equity Offering Sales Agreement Maximum	Sep. 30, 2013 Series B Preferred Stock	Sep. 30, 2013 Series B Preferred Stock Controlled Equity Offering Sales Agreement	May 27, 2011 Series B Preferred Stock Controlled Equity Offering Sales Agreement Maximum	Sep. 30, 2013 Common Stock Controlled Equity Offering Sales Agreement	May 27, 2011 Common Stock Controlled Equity Offering Sales Agreement Maximum
Capital Unit [Line Items]
Common Stock, authorized	200,000,000			200,000,000		200,000,000
Common Stock, issued	141,603,000			141,603,000		142,013,000				2,832,000
Common Stock, outstanding	141,603,000			141,603,000		142,013,000
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			$ 25		$ 25										$ 25.00			$ 25.00
Preferred Stock, dividend rate																8.625%			6.25%
Preferred stock, issued	1,919,000			1,919,000		1,877,000										1,919,378			1,009,640
Preferred stock, outstanding	1,919,000			1,919,000		1,877,000										1,919,378			1,009,640
Number of shares to be issued based on sales agreement																		1,000,000			1,000,000		20,000,000
Common Stock, available for issuance																						19,409,400
Preferred stock, available for sale and issuance																	956,122			894,518
Preferred stock redemption price																$ 25.00
Number of shares authorized to be repurchased							2,000,000
Shares repurchased during period	1,472,710
Stock repurchased, weighted average price per share	$ 4.53
Public offering number of common stocks															27,000,000
Issuance of common stock (in shares)								723,499
Common stock issued, weighted average price per share								$ 4.98
Proceeds from issuance of common stock	$ (3,085,000)		$ 21,644,000	$ (2,560,000)	$ 47,432,000			$ 3,600,000
Remaining number of shares to be issued								16,849,000	16,849,000
Effective discount rate on dividend									0.00%				1.00%
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											3,500,000	3,500,000
Unexercised stock options and restricted stock										475,142