Related Party Transactions - Additional Information (Detail) - USD ($) | 1 Months Ended | 9 Months Ended | 11 Months Ended |
Dec. 31, 2016 | Sep. 30, 2017 | Sep. 30, 2017 |
Related Party Transaction [Line Items] | | | |
Performance fee percentage | | 10.00% | |
Hurdle rate on average adjusted capital | | 1.625% | |
Annualized hurdle rate | | 6.50% | |
Quarterly core earnings rate | | 1.806% | |
Annualized core earnings rate | | 7.222% | |
Organization costs incurred | | | $ 243,000 |
Offering costs incurred | | | 2,369,000 |
Minimum gross proceeds from public offering to reimburse expense | | $ 250,000,000 | $ 250,000,000 |
Stock issued during period | $ 200,000 | 17,868,000 | |
Common Class S [Member] | | | |
Related Party Transaction [Line Items] | | | |
Base management fee | | 0 | |
Performance fees on shares | | $ 0 | |
Number of common shares issued | 8,000 | 560,000 | |
Stock issued during period | $ 0 | $ 6,000 | |
Common Class Y [Member] | | | |
Related Party Transaction [Line Items] | | | |
Base management fee | | $ 0 | |
Number of common shares issued | | 154,720 | |
Stock issued during period | | $ 2,000 | |
Maximum [Member] | | | |
Related Party Transaction [Line Items] | | | |
Organization and offering expenses reimbursement as percentage of gross proceeds from public offering | | 15.00% | 15.00% |
FS Real Estate Advisor [Member] | | | |
Related Party Transaction [Line Items] | | | |
Base management fee percentage | | 1.25% | |
Base management fee description | | Accrues daily equal to 1/365th of 1.25% of the NAV for the Company's Class T, Class T-C, Class D, Class M and Class I shares for such day, payable quarterly and in arrears. | |
Percentage of base management fees and performance fees payable to advisor | | 50.00% | |
Payment financing costs | | $ 100,000 | |
FS Real Estate Advisor [Member] | Common Class S [Member] | | | |
Related Party Transaction [Line Items] | | | |
Stockholders servicing fee | | 0 | |
FS Real Estate Advisor [Member] | Common Class Y [Member] | | | |
Related Party Transaction [Line Items] | | | |
Stockholders servicing fee | | $ 0 | |
FS Real Estate Advisor [Member] | Common Class T [Member] | | | |
Related Party Transaction [Line Items] | | | |
Dealer manager upfront selling commissions fees percentage | | 3.00% | |
Upfront dealer manager fees percentage | | 1.25% | |
Stockholders servicing fee percentage on aggregate NAV of outstanding shares | | 1.00% | |
FS Real Estate Advisor [Member] | Common Class T - C [Member] | | | |
Related Party Transaction [Line Items] | | | |
Dealer manager upfront selling commissions fees percentage | | 3.00% | |
Stockholders servicing fee percentage on aggregate NAV of outstanding shares | | 0.85% | |
Advisor stockholders servicing fee percentage on aggregate NAV of outstanding shares | | 0.60% | |
Dealer stockholders servicing fee percentage on aggregate NAV of outstanding shares | | 0.25% | |
FS Real Estate Advisor [Member] | Common Class D [Member] | | | |
Related Party Transaction [Line Items] | | | |
Stockholders servicing fee percentage on aggregate NAV of outstanding shares | | 0.30% | |
FS Real Estate Advisor [Member] | Common Class M [Member] | | | |
Related Party Transaction [Line Items] | | | |
Stockholders servicing fee percentage on aggregate NAV of outstanding shares | | 0.30% | |
FS Real Estate Advisor [Member] | Class D, Class M, Class I, Class S Or Class Y Shares [Member] | | | |
Related Party Transaction [Line Items] | | | |
Selling commissions or dealer manager fees payable | | $ 0 | |
FS Real Estate Advisor [Member] | Common Class I [Member] | | | |
Related Party Transaction [Line Items] | | | |
Stockholders servicing fee | | $ 0 | |
FS Real Estate Advisor [Member] | Class D Share [Member] | | | |
Related Party Transaction [Line Items] | | | |
Stockholder servicing fees percentage | | 1.25% | 1.25% |
FS Real Estate Advisor [Member] | Class T, Class T-C and Class M Shares [Member] | | | |
Related Party Transaction [Line Items] | | | |
Stockholder servicing fees percentage | | 7.25% | 7.25% |
FS Real Estate Advisor [Member] | Maximum [Member] | | | |
Related Party Transaction [Line Items] | | | |
Organization and offering expenses reimbursement as percentage of gross proceeds from public offering | | 0.75% | 0.75% |
FS Real Estate Advisor and Rialto [Member] | Expense Limitation Agreement [Member] | | | |
Related Party Transaction [Line Items] | | | |
Percentage of minimum operating expenses to be waived or paid | | 1.50% | |
FS Real Estate Advisor and Rialto [Member] | Private Placement [Member] | | | |
Related Party Transaction [Line Items] | | | |
Aggregate proceeds from private placement | $ 200,000 | | |
Number of common shares issued | 8,000 | | |
Common stock, price per share | $ 25 | | |
FS Real Estate Advisor and Rialto [Member] | Common Class S [Member] | Private Placement [Member] | | | |
Related Party Transaction [Line Items] | | | |
Common stock allocated to investors | | $ 50,000,000 | $ 50,000,000 |
Common stock, price per share | | $ 25 | $ 25 |
Net assets | | $ 750,000,000 | $ 750,000,000 |
Stock issued during period | | $ 14,000,000 | |
FS Real Estate Advisor and Rialto [Member] | Maximum [Member] | Expense Limitation Agreement [Member] | | | |
Related Party Transaction [Line Items] | | | |
Period for which reimbursement payable | | 3 years | |
FS Real Estate Advisor and Rialto [Member] | Minimum [Member] | Common Class S [Member] | Private Placement [Member] | | | |
Related Party Transaction [Line Items] | | | |
Investments to be maintained | | $ 10,000,000 | $ 10,000,000 |
Rialto [Member] | | | |
Related Party Transaction [Line Items] | | | |
Purchase of floating-rate whole mortgage loan | | $ 9,500,000 | |