Merger with Tremont Mortgage Trust - Summary of Consideration Transferred and Liabilities Assumed (Details) - TRMT Merger - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Sep. 30, 2021	Dec. 31, 2021
Asset Acquisition [Line Items]
TRMT common shares outstanding (in shares)	8,303,629
Exchange ratio of shares issued per acquiree share ( in shares)	0.516	0.516
SEVN Common Shares issued, before adjustment (in shares)	4,284,673
TRMT fractional shares adjustment (in shares)	(73)
SEVN common shares issued (in shares)	4,284,600
Share price (in dollars per share)	$ 10.31
Value of consideration transferred	$ 44,174
Assumed working capital	(10,146)
Assumed Citibank Master Repurchase Facility, principal balance	128,962
Merger related costs	6,160
Consideration transferred and liabilities assumed	$ 169,150