v3.20.2

Mortgages and Notes Payable - Summary of Extinguished Mortgages (Detail) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2020 USD ($) Mortgage	Dec. 31, 2019 USD ($) Mortgage
Debt Disclosure [Abstract]
Number of mortgages | Mortgage	1	4
Outstanding balance of mortgages | $	$ 541	$ 13,905

X

- Definition

Number of mortgages extinguished.

+ References

No definition available.

+ Details

Name:	ck1424182_NumberOfMortgagesExtinguished
Namespace Prefix:	ck1424182_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

- References

No definition available.

+ Details

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

X

- Definition

Gross amount of debt extinguished.

+ References

No definition available.

+ Details

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