Subsequent Event - Additional Information (Details) $ / shares in Units, $ in Thousands		3 Months Ended	12 Months Ended
	Apr. 10, 2016 USD ($) $ / shares shares	Mar. 31, 2016 $ / shares	Dec. 31, 2015 $ / shares
Subsequent Event [Line Items]
Preferred stock dividend rate per year		7.625%	7.625%
Preferred stock, par value		$ 0.001	$ 0.001
7.625% Series A Cumulative Redeemable Preferred Stock
Subsequent Event [Line Items]
Preferred stock dividend rate per year		7.625%
Preferred stock, par value		$ 0.001
Subsequent Event | ACA
Subsequent Event [Line Items]
Termination fee | $	$ 45,411
Subsequent Event | Annaly Capital Management Inc
Subsequent Event [Line Items]
Business acquisition, agreement date	Apr. 10, 2016
Percentage of aggregate consideration payable to holders of company's common stock in the form of common stock	65.00%
Percentage of aggregate consideration payable to holders of company's common stock in the form of cash	35.00%
Percentage of outstanding shares of common stock	0.6667%
Termination fee | $	$ 44,949
Subsequent Event | Annaly Capital Management Inc | Cumulative Redeemable Series E Preferred Stock
Subsequent Event [Line Items]
Preferred stock dividend rate per year	7.625%
Preferred stock, par value	$ 0.01
Each share converted to newly-designated series of Annaly Preferred stock | shares	1
Subsequent Event | Annaly Capital Management Inc | Mixed Consideration Option
Subsequent Event [Line Items]
Business acquisition, per share	$ 5.55
Common stock shares issuable for each share	0.9894
Subsequent Event | Annaly Capital Management Inc | Cash Consideration Option
Subsequent Event [Line Items]
Business acquisition, per share	$ 15.85
Subsequent Event | Annaly Capital Management Inc | Stock Consideration Option
Subsequent Event [Line Items]
Common stock shares issuable for each share	1.5226