INCOME TAXES - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Net operating loss	$ 90,000
Percentage of taxable income offset by tax losses	80.00%
Description of tax credit carryforward	Additionally, the CARES Act modified the rules for REIT net operating losses (“NOL”). A REIT NOL carryover can now only offset 80% of taxable income for losses arising in years beginning after December 31, 2020. The 80% limitation is calculated by multiplying current-year REIT taxable income before the dividends paid deduction by 80%. For tax years beginning before January 1, 2021, a taxpayer can offset 100% of its income in any given year with an NOL.  Although there will be an annual NOL limitation for tax years starting after December 31, 2020, the Tax Act allows post-2017 NOLs to be carried forward indefinitely. At December 31, 2020 Capstead had an NOL of $90 million that does not expire.
Income taxes paid	$ 0	$ 0	$ 0
Net capital loss carryforwards	$ 68,200	$ 17,500
Capital loss carryforwards, expiration date	Dec. 31, 2025	Dec. 31, 2019