Percent of amount of paid and unpaid common stock dividends declared with the form of settlement in cash

No definition available.

Name:	cik0001690536_DividendsCommonStockCashPercent
Namespace Prefix:	cik0001690536_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percent of amount of paid and unpaid common stock dividends declared with the form of settlement in cash, stock and payment-in-kind (PIK).

+ References

No definition available.

+ Details

Name:	cik0001690536_DividendsCommonStockPercent
Namespace Prefix:	cik0001690536_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percent of cash inflow associated with the amount received from entity's first offering of stock to the public.

+ References

No definition available.

+ Details

Name:	cik0001690536_ProceedsFromIssuanceInitialPublicOfferingPercent
Namespace Prefix:	cik0001690536_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Stock Issued During Period Value Dividend Reinvestment Plan Cash Impact

+ References

No definition available.

+ Details

Name:	cik0001690536_StockIssuedDuringPeriodValueDividendReinvestmentPlanCashImpact
Namespace Prefix:	cik0001690536_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Percent of stock Issued During Period Value Dividend Reinvestment Plan Cash Impact

+ References

No definition available.

+ Details

Name:	cik0001690536_StockIssuedDuringPeriodValueDividendReinvestmentPlanCashImpactPercent
Namespace Prefix:	cik0001690536_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Aggregate dividends paid during the period for each share of common stock outstanding.

+ References

+ Details

Name:	us-gaap_CommonStockDividendsPerShareCashPaid
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of paid and unpaid common stock dividends declared with the form of settlement in cash, stock and payment-in-kind (PIK).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 405
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6957935&loc=d3e64057-112817

+ Details

Name:	us-gaap_DividendsCommonStock
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- References

No definition available.

+ Details

Name:	us-gaap_DividendsCommonStockAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of paid and unpaid common stock dividends declared with the form of settlement in cash.

+ References

+ Details

Name:	us-gaap_DividendsCommonStockCash
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Date the holder must own the stock to be entitled to the dividend, in CCYY-MM-DD format.

+ References

No definition available.

+ Details

Name:	us-gaap_DividendsPayableDateOfRecordDayMonthAndYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DividendsPayableLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of cash inflow (outflow) from operating activities, including discontinued operations. Operating activity cash flows include transactions, adjustments, and changes in value not defined as investing or financing activities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 25
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3536-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 24
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3521-108585

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

+ Details

Name:	us-gaap_NetCashProvidedByUsedInOperatingActivities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash inflow associated with the amount received from entity's first offering of stock to the public.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3255-108585

+ Details

Name:	us-gaap_ProceedsFromIssuanceInitialPublicOffering
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_StatementClassOfStockAxis=cik0001690536_CommonClassFMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementClassOfStockAxis=cik0001690536_CommonClassYMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementClassOfStockAxis=cik0001690536_CommonClassTMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementClassOfStockAxis=cik0001690536_CommonClassSMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementClassOfStockAxis=cik0001690536_CommonClassDMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementClassOfStockAxis=cik0001690536_CommonClassMMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementClassOfStockAxis=cik0001690536_CommonClassIMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Stockholders' Equity - Summary of Cash Distributions Per Share that Paid on its Common Stock (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended												12 Months Ended
	Dec. 28, 2018	Nov. 29, 2018	Oct. 30, 2018	Sep. 27, 2018	Aug. 30, 2018	Jul. 30, 2018	Jun. 28, 2018	May 30, 2018	Apr. 27, 2018	Mar. 29, 2018	Feb. 27, 2018	Jan. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Dividends Payable [Line Items]
Dividend record date	Dec. 28, 2018	Nov. 29, 2018	Oct. 30, 2018	Sep. 27, 2018	Aug. 30, 2018	Jul. 30, 2018	Jun. 28, 2018	May 30, 2018	Apr. 27, 2018	Mar. 29, 2018	Feb. 27, 2018	Jan. 30, 2018
Distributions:
Paid or payable in cash													$ 1,488	$ 79
Reinvested in shares													2,459	328
Total distributions													$ 3,947	$ 407
Paid or payable in cash in percent													38.00%	19.00%
Reinvested in shares in percent													62.00%	81.00%
Total distributions in percent													100.00%	100.00%
Cash flows from operating activities													$ 3,947	$ 407
Offering proceeds													0	0
Total sources of distributions													3,947	407
Net cash provided by operating activities													$ 5,198	$ 579
Cash flows from operating activities in percent													100.00%	100.00%
Offering proceeds in percent													0.00%	0.00%
Total sources of distributions in percent													100.00%	100.00%
Common Class F [Member]
Dividends Payable [Line Items]
Distributions paid per share of common stock	$ 0.1510	$ 0.1510	$ 0.1510	$ 0.1510	$ 0.1510	$ 0.1510	$ 0.1510	$ 0.1510	$ 0.1510	$ 0.1510	$ 0.1510	$ 0.1510	$ 1.8120
Common Class Y [Member]
Dividends Payable [Line Items]
Distributions paid per share of common stock	0.1510	0.1510	0.1510	0.1510	0.1510	0.1510	0.1510	0.1510	0.1510	0.1510	0.1510	0.1510	1.8120
Common Class T [Member]
Dividends Payable [Line Items]
Distributions paid per share of common stock	0.1073	0.1073	0.1073	0.1042	0.1042	0.1042	0.1376	0.0946	0.1424				1.0091
Common Class S [Member]
Dividends Payable [Line Items]
Distributions paid per share of common stock	0.1073	0.1073	0.1073	0.1073	0.1073	0.1073	0.1087	0.1182					0.8707
Common Class D [Member]
Dividends Payable [Line Items]
Distributions paid per share of common stock	0.1188	0.1188	0.1188	0.1188	0.1188	0.1188	0.1370	0.1298	0.1434				1.1230
Common Class M [Member]
Dividends Payable [Line Items]
Distributions paid per share of common stock	0.1188	0.1188	0.1188	0.1188	0.1188	0.1188	0.1234	0.1394					0.9756
Common Class I [Member]
Dividends Payable [Line Items]
Distributions paid per share of common stock	$ 0.1250	$ 0.1250	$ 0.1250	$ 0.1250	$ 0.1250	$ 0.1250	$ 0.1276	$ 0.1258	$ 0.1296	$ 0.1510	$ 0.1510	$ 0.1510	$ 1.5860