v3.8.0.1

Interest Rate Swaps - Summary of Interest-rate Swap Agreements (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2017
Interest Rate Swap | M&T Bank One | Umbrella Partnership Real Estate Investment Trust Transaction
Derivative [Line Items]
Interest rate swap assumed month and year	2017-10

X

- Definition

Interest rate swap assumed month and year.

+ References

No definition available.

+ Details

Name:	ck0001424182_InterestRateSwapAssumedMonthAndYear
Namespace Prefix:	ck0001424182_
Data Type:	xbrli:gYearMonthItemType
Balance Type:	na
Period Type:	duration

X

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

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_CounterpartyNameAxis=ck0001424182_MAndTBankOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	invest_InvestmentAxis=ck0001424182_UmbrellaPartnershipRealEstateInvestmentTrustTransactionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: