Secured Notes Payable and Revolving Credit Facility, Net - Schedule of Secured Notes Payable and Revolving Credit Facility (Details) - USD ($)	9 Months Ended
Sep. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Principal Balance	$ 4,154,157,000	$ 4,152,308,000
Unamortized loan premium, net	4,037,000	4,191,000
Deferred loan costs, net	(35,917,000)	(39,109,000)
Total Consolidated Debt, Net	4,122,277,000	4,117,390,000
Revolving Credit Facility With Maturity Date of August 21, 2020
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 400,000,000
Revolving Credit Facility With Maturity Date of August 21, 2020 \| Minimum
Debt Instrument [Line Items]
Unused commitment fees (as a percent)	0.15%
Revolving Credit Facility With Maturity Date of August 21, 2020 \| Maximum
Debt Instrument [Line Items]
Unused commitment fees (as a percent)	0.20%
Secured Debt \| LIBOR \| Minimum
Debt Instrument [Line Items]
Basis Spread on Variable Rate	0.00%
Secured Debt \| Term Loan With Maturity Date of June 1, 2038
Debt Instrument [Line Items]
Fixed Rate Debt Amortization Period	30 years
Wholly Owned Subsidiaries
Debt Instrument [Line Items]
Principal Balance	$ 3,174,157,000	3,172,308,000
Wholly Owned Subsidiaries \| Secured Debt \| Term Loan With Effective Annual Fixed Interest Rate At 4.00%
Debt Instrument [Line Items]
Principal Balance	0	146,974,000
Wholly Owned Subsidiaries \| Secured Debt \| Term Loan With Effective Annual Fixed Interest Rate At 3.85%
Debt Instrument [Line Items]
Principal Balance	$ 0	280,721,000
Wholly Owned Subsidiaries \| Secured Debt \| Fannie Mae Loan With Maturity Date of October 1, 2019
Debt Instrument [Line Items]
Maturity Date	Oct. 01, 2019
Principal Balance	$ 145,000,000	145,000,000
Variable Interest Rate	LIBOR + 1.25%
Wholly Owned Subsidiaries \| Secured Debt \| Fannie Mae Loan With Maturity Date of October 1, 2019 \| LIBOR
Debt Instrument [Line Items]
Basis Spread on Variable Rate	1.25%
Wholly Owned Subsidiaries \| Secured Debt \| Term Loan With Effective Annual Fixed Interest Rate At 2.77%
Debt Instrument [Line Items]
Maturity Date	Apr. 15, 2022
Principal Balance	$ 340,000,000	340,000,000
Variable Interest Rate	LIBOR + 1.40%
Fixed Interest Rate	2.77%
Swap Maturity Date	Apr. 01, 2020
Wholly Owned Subsidiaries \| Secured Debt \| Term Loan With Effective Annual Fixed Interest Rate At 2.77% \| LIBOR
Debt Instrument [Line Items]
Basis Spread on Variable Rate	1.40%
Wholly Owned Subsidiaries \| Secured Debt \| Term Loan With Effective Annual Fixed Interest Rate At 3.06%
Debt Instrument [Line Items]
Maturity Date	Jul. 27, 2022
Principal Balance	$ 180,000,000	180,000,000
Variable Interest Rate	LIBOR + 1.45%
Fixed Interest Rate	3.06%
Swap Maturity Date	Jul. 01, 2020
Wholly Owned Subsidiaries \| Secured Debt \| Term Loan With Effective Annual Fixed Interest Rate At 3.06% \| LIBOR
Debt Instrument [Line Items]
Basis Spread on Variable Rate	1.45%
Wholly Owned Subsidiaries \| Secured Debt \| Term Loan With Effective Annual Fixed Interest Rate At 2.64%
Debt Instrument [Line Items]
Maturity Date	Nov. 01, 2022
Principal Balance	$ 400,000,000	400,000,000
Variable Interest Rate	LIBOR + 1.35%
Fixed Interest Rate	2.64%
Swap Maturity Date	Nov. 01, 2020
Wholly Owned Subsidiaries \| Secured Debt \| Term Loan With Effective Annual Fixed Interest Rate At 2.64% \| LIBOR
Debt Instrument [Line Items]
Basis Spread on Variable Rate	1.35%
Wholly Owned Subsidiaries \| Secured Debt \| Term Loan With Effective Annual Fixed Interest Rate At 2.57%
Debt Instrument [Line Items]
Maturity Date	Jun. 23, 2023
Principal Balance	$ 360,000,000	360,000,000
Variable Interest Rate	LIBOR + 1.55%
Fixed Interest Rate	2.57%
Swap Maturity Date	Jul. 01, 2021
Wholly Owned Subsidiaries \| Secured Debt \| Term Loan With Effective Annual Fixed Interest Rate At 2.57% \| LIBOR
Debt Instrument [Line Items]
Basis Spread on Variable Rate	1.55%
Wholly Owned Subsidiaries \| Secured Debt \| Term Loan With Effective Annual Fixed Interest Rate At 3.62%
Debt Instrument [Line Items]
Maturity Date	Dec. 23, 2023
Principal Balance	$ 220,000,000	220,000,000
Variable Interest Rate	LIBOR + 1.70%
Fixed Interest Rate	3.62%
Swap Maturity Date	Dec. 23, 2021
Wholly Owned Subsidiaries \| Secured Debt \| Term Loan With Effective Annual Fixed Interest Rate At 3.62% \| LIBOR
Debt Instrument [Line Items]
Basis Spread on Variable Rate	1.70%
Wholly Owned Subsidiaries \| Secured Debt \| Term Loan With Effective Annual Fixed Interest Rate At 3.46%
Debt Instrument [Line Items]
Maturity Date	Jan. 01, 2024
Principal Balance	$ 300,000,000	300,000,000
Variable Interest Rate	LIBOR + 1.55%
Fixed Interest Rate	3.46%
Swap Maturity Date	Jan. 01, 2022
Wholly Owned Subsidiaries \| Secured Debt \| Term Loan With Effective Annual Fixed Interest Rate At 3.46% \| LIBOR
Debt Instrument [Line Items]
Basis Spread on Variable Rate	1.55%
Wholly Owned Subsidiaries \| Secured Debt \| Term Loan With Effective Annual Fixed Interest Rate At 3.84%
Debt Instrument [Line Items]
Maturity Date	Mar. 03, 2025
Principal Balance	$ 335,000,000	0
Variable Interest Rate	LIBOR + 1.30%
Fixed Interest Rate	3.84%
Swap Maturity Date	Mar. 01, 2023
Wholly Owned Subsidiaries \| Secured Debt \| Term Loan With Effective Annual Fixed Interest Rate At 3.84% \| LIBOR
Debt Instrument [Line Items]
Basis Spread on Variable Rate	1.30%
Wholly Owned Subsidiaries \| Secured Debt \| Fannie Mae Loan With Maturity Date of April 1, 2025
Debt Instrument [Line Items]
Maturity Date	Apr. 01, 2025
Principal Balance	$ 102,400,000	102,400,000
Variable Interest Rate	LIBOR + 1.25%
Fixed Interest Rate	2.84%
Swap Maturity Date	Mar. 01, 2020
Wholly Owned Subsidiaries \| Secured Debt \| Fannie Mae Loan With Maturity Date of April 1, 2025 \| LIBOR
Debt Instrument [Line Items]
Basis Spread on Variable Rate	1.25%
Wholly Owned Subsidiaries \| Secured Debt \| Fannie Mae Loans With Maturity Date of December 1, 2025
Debt Instrument [Line Items]
Maturity Date	Dec. 01, 2025
Principal Balance	$ 115,000,000	115,000,000
Variable Interest Rate	LIBOR + 1.25%
Fixed Interest Rate	2.76%
Swap Maturity Date	Dec. 01, 2020
Wholly Owned Subsidiaries \| Secured Debt \| Fannie Mae Loans With Maturity Date of December 1, 2025 \| LIBOR
Debt Instrument [Line Items]
Basis Spread on Variable Rate	1.25%
Wholly Owned Subsidiaries \| Secured Debt \| Fannie Mae Loans With Maturity Date of June 1, 2027
Debt Instrument [Line Items]
Maturity Date	Jun. 01, 2027
Principal Balance	$ 550,000,000	550,000,000
Variable Interest Rate	LIBOR + 1.37%
Fixed Interest Rate	3.16%
Swap Maturity Date	Jun. 01, 2022
Wholly Owned Subsidiaries \| Secured Debt \| Fannie Mae Loans With Maturity Date of June 1, 2027 \| LIBOR
Debt Instrument [Line Items]
Basis Spread on Variable Rate	1.37%
Wholly Owned Subsidiaries \| Secured Debt \| Term Loan With Maturity Date of June 1, 2038
Debt Instrument [Line Items]
Maturity Date	Jun. 01, 2038
Principal Balance	$ 31,757,000	32,213,000
Fixed Interest Rate	4.55%
Wholly Owned Subsidiaries \| Line of Credit \| Revolving Credit Facility With Maturity Date of August 21, 2020
Debt Instrument [Line Items]
Maturity Date	Aug. 21, 2020
Principal Balance	$ 95,000,000	0
Variable Interest Rate	LIBOR + 1.40%
Wholly Owned Subsidiaries \| Line of Credit \| Revolving Credit Facility With Maturity Date of August 21, 2020 \| LIBOR
Debt Instrument [Line Items]
Basis Spread on Variable Rate	1.40%
Consolidated JV \| Secured Debt \| Term Loan With Maturity Date of February 28, 2023
Debt Instrument [Line Items]
Maturity Date	Feb. 28, 2023
Principal Balance	$ 580,000,000	580,000,000
Variable Interest Rate	LIBOR + 1.40%
Fixed Interest Rate	2.37%
Swap Maturity Date	Mar. 01, 2021
Consolidated JV \| Secured Debt \| Term Loan With Maturity Date of February 28, 2023 \| LIBOR
Debt Instrument [Line Items]
Basis Spread on Variable Rate	1.40%
Consolidated JV \| Secured Debt \| Term Loan With Maturity Date of December 19, 2024
Debt Instrument [Line Items]
Maturity Date	Dec. 19, 2024
Principal Balance	$ 400,000,000	$ 400,000,000
Variable Interest Rate	LIBOR + 1.30%
Fixed Interest Rate	3.47%
Swap Maturity Date	Jan. 01, 2023
Consolidated JV \| Secured Debt \| Term Loan With Maturity Date of December 19, 2024 \| LIBOR
Debt Instrument [Line Items]
Basis Spread on Variable Rate	1.30%

Fixed Rate Debt Amortization Period

No definition available.

Name:	nysedei_FixedRateDebtAmortizationPeriod
Namespace Prefix:	nysedei_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6031897-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Name:	us-gaap_DebtInstrumentCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

+ References

No definition available.

+ Details

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

- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

+ Details

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

- Definition

Amount, after accumulated amortization, of debt premium.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28541-108399

+ Details

Name:	us-gaap_DebtInstrumentUnamortizedPremium
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28555-108399

+ Details

Name:	us-gaap_DeferredFinanceCostsNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fixed interest rate related to the interest rate derivative.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeFixedInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Date the derivative contract matures, in CCYY-MM-DD format.

+ References

No definition available.

+ Details

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

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6031897-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LongTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_DebtInstrumentAxis=nysedei_RevolvingCreditFacilityWithMaturityDate82120Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SecuredDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=nysedei_TermLoanWithMaturityDateOfJune12038Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidatedEntitiesAxis=srt_SubsidiariesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=nysedei_TermLoanWithEffectiveAnnualFixedInterestRateAtFourPointZeroZeroPercentageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=nysedei_TermLoanWithEffectiveAnnualFixedInterestRateAtThreePointEightFivePercentageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=nysedei_FannieMaeLoansMaturityDateOctober12019Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=nysedei_TermLoanWithEffectiveAnnualFixedInterestRateAtTwoPointSevenSevenPercentageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=nysedei_TermLoanWithEffectiveAnnualFixedInterestRateAtThreePointZeroSixPercentageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=nysedei_TermLoanWithEffectiveAnnualFixedInterestRateAtTwoPointSixFourPercentageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=nysedei_TermLoanWithEffectiveAnnualFixedInterestRateAtTwoPointFiveSevenPercentageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=nysedei_TermLoanWithEffectiveAnnualFixedInterestRateAtThreePointSixTwoPercentageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=nysedei_TermLoanWithEffectiveAnnualFixedInterestRateAtThreePointFourSixPercentageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=nysedei_TermLoanWithEffectiveAnnualFixedInterestRateAtThreePointEightFourPercentageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=nysedei_FannieMaeLoanWithMaturityDateOfApril12025Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=nysedei_FannieMaeLoanswithMaturityDateofDecember12025Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=nysedei_FannieMaeLoanswithMaturityDateofJune12027Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_LineOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidatedEntitiesAxis=srt_AffiliatedEntityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=nysedei_TermLoanwithMaturityDateofFebruary282023Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=nysedei_TermLoanWithMaturityDateOfDecember192024Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: