Schedule of Net Income (Loss) Per Share Reconciliation (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Net Income Per Common Share:
Net income (loss)	$ (278,497)	$ 900,071	$ (1,146,577)	$ 423,572
Less: Net income (loss) attributable to noncontrolling interest	(385)	(149)	(547)	(239)
Net income (loss) attributable to Annaly	(278,112)	900,220	(1,146,030)	423,811
Less: Preferred stock dividends	17,992	17,992	35,984	35,984
Net income (loss) available (related) to common stockholders, prior to adjustment for dilutive potential common shares, if necessary	(296,104)	882,228	(1,182,014)	387,827
Add: Interest on Convertible Senior Notes, if dilutive	0	0	0	0
Net income (loss) available to common stockholders, as adjusted	$ (296,104)	$ 882,228	$ (1,182,014)	$ 387,827
Weighted average shares of common stock outstanding-basic	924,887,316	947,731,493	925,850,452	947,700,832
Add: Effect of stock awards and Convertible Senior Notes, if dilutive		198,269		178,126
Weighted average shares of common stock outstanding-diluted	924,887,316	947,929,762	925,850,452	947,878,958
Net income (loss) per share available (related) to common share:
Basic	$ (0.32)	$ 0.93	$ (1.28)	$ 0.41
Diluted	$ (0.32)	$ 0.93	$ (1.28)	$ 0.41