INCOME TAXES - Schedule of Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Effective income tax rate reconciliation [Abstract]
Income taxes computed at the federal statutory rate	$ 29,005	$ 37,914	$ 49,287
Benefit of REIT status	(29,003)	(37,913)	(49,283)
Income taxes computed on income of Capstead’s sole taxable REIT subsidiary	2	1	4
Change in net deferred income tax assets	(2)	(1)	(4)
Income tax provision	$ 0	$ 0	$ 0