Quarterly report pursuant to Section 13 or 15(d)

Acquisition of CYS Investments, Inc. Calculation of the Purchase Price of CYS Investments, Inc. (Details)

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Acquisition of CYS Investments, Inc. Calculation of the Purchase Price of CYS Investments, Inc. (Details)
 1 Months Ended 9 Months Ended
Jul. 31, 2018
USD ($)
$ / shares
shares
Sep. 30, 2018
USD ($)
shares
Sep. 30, 2017
shares
Dec. 31, 2017
USD ($)
shares
Dec. 31, 2016
shares
Business Acquisition, Equity Interests Issued or Issuable [Line Items]          
Total Purchase Price | $ $ 1,415,084,000        
Common stock share price (in usd per share) | $ / shares $ 15.50        
CYS common shares outstanding (in shares) | shares   248,078,170   174,496,587  
Exchange ratio for number of shares of Two Harbors common stock issued 0.4680        
Number of shares of common stock issuable in connection with the acquisition of CYS Investments, Inc. (in shares) | shares 72,587,990        
Number of fractional shares of common stock not issued in connection with the acquisition of CYS Investments, Inc. (in shares) | shares 218        
Value of common stock issued in connection with the acquisition of CYS Investments, Inc. | $   $ 1,400,114,000      
Price per share paid to CYS common stockholders for fractional shares not issued in connection with the acquisition (in usd per share) | $ / shares $ 15.59        
Total cash paid to CYS common stockholders for fractional shares not issued in connection with the acquisition | $ $ 3,000        
Cash consideration provided to CYS common stockholders (in usd per share) | $ / shares $ 0.0965        
Aggregate cash consideration exchanged for shares of CYS common stock | $ $ 14,967,000        
Preferred stock liquidation preference | $   $ 1,001,250,000   $ 726,250,000  
CYS Investments, Inc. [Member]          
Business Acquisition, Equity Interests Issued or Issuable [Line Items]          
CYS common shares outstanding (in shares) | shares 155,102,543        
Common Stock [Member]          
Business Acquisition, Equity Interests Issued or Issuable [Line Items]          
CYS common shares outstanding (in shares) | shares   248,078,170 174,489,356 174,496,587 173,826,163
Number of shares of stock issued during period (in shares) | shares 72,587,772 72,608,932 19,688    
Series D Preferred Stock [Member]          
Business Acquisition, Equity Interests Issued or Issuable [Line Items]          
Number of shares of stock issued during period (in shares) | shares 3,000,000        
Preferred stock liquidation preference | $ $ 75,000,000        
Series E Preferred Stock [Member]          
Business Acquisition, Equity Interests Issued or Issuable [Line Items]          
Number of shares of stock issued during period (in shares) | shares 8,000,000        
Preferred stock liquidation preference | $ $ 200,000,000        
Common Stock Including Additional Paid in Capital          
Business Acquisition, Equity Interests Issued or Issuable [Line Items]          
Value of common stock issued in connection with the acquisition of CYS Investments, Inc. | $ $ 1,125,114,000