Schedule of Net Income (Loss) Per Share Reconciliation (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015
Net Income Per Common Share:
Net income (loss)	$ (868,080)	$ (476,499)	$ (476,499)
Less: Net income (loss) attributable to noncontrolling interest	(162)	(90)	(90)
Net income (loss) attributable to Annaly	(867,918)	(476,409)	(476,409)
Less: Preferred stock dividends	17,992	17,992	17,992
Net income (loss) per share available (related) to common stockholders, prior to adjustment for dilutive potential common shares, if necessary	(885,910)	(494,401)	$ (494,401)
Add: Interest on Convertible Senior Notes, if dilutive	0	0
Net income (loss) available to common stockholders, as adjusted	$ (885,910)	$ (494,401)
Weighted average shares of common stock outstanding-basic	926,813,588	947,669,831	947,669,831
Add: Effect of stock awards and Convertible Senior Notes, if dilutive	0	0
Weighted average shares of common stock outstanding-diluted	926,813,588	947,669,831	947,669,831
Net income (loss) per share available (related) to common share:
Basic	$ (0.96)	$ (0.52)	$ (0.52)
Diluted	$ (0.96)	$ (0.52)	$ (0.52)