Debt instrument discount interest rate percentage.

No definition available.

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- Definition

Debt instrument interest coverage ratio.

+ References

No definition available.

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- Definition

Debt instrument leverage ratio percentage.

+ References

No definition available.

+ Details

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- Definition

Indenture covenant percentage on unencumbered assets.

+ References

No definition available.

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- Definition

Unsecured line of credit and term notes.

+ References

No definition available.

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- Definition

Amount of amortization expense attributable to debt issuance costs.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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- Definition

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

+ References

No definition available.

+ Details

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- 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
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- Definition

Face (par) amount of debt instrument at time of issuance.

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

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- Definition

Amount, after accumulated amortization, of debt discount.

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- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

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- Definition

Date the credit facility terminates, in CCYY-MM-DD format.

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- Definition

The effective interest rate at the end of the reporting period.

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- 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.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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- 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
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Period Type:	instant

- Definition

The interest rate applicable to the portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a rate subject to change from time to time.

+ References

+ Details

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- Definition

The cash outflow paid to third parties in connection with debt origination, which will be amortized over the remaining maturity period of the associated long-term debt.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (e)
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Balance Type:	credit
Period Type:	duration

- Definition

The cash inflow during the period from additional borrowings in aggregate debt. Includes proceeds from short-term and long-term debt.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
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Balance Type:	debit
Period Type:	duration

- Definition

The cash inflow from a borrowing with the highest claim on the assets of the entity in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle, if longer).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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-SubTopic 10
-Section 45
-Paragraph 14
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The cash outflow to repay long-term debt that is not secured by collateral. Excludes repayments of tax exempt unsecured debt.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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Unsecured Line of Credit and Term Notes - Additional Information (Detail) - USD ($)					3 Months Ended		6 Months Ended		12 Months Ended
	Dec. 07, 2017	Jul. 21, 2016	Jun. 20, 2016	Apr. 08, 2014	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2011	Dec. 31, 2017
Unsecured Line Of Credit And Term Notes [Line Items]
Unsecured term note					$ 1,625,000,000		$ 1,625,000,000			$ 1,625,000,000
Term notes, outstanding amount					1,750,489,000		1,750,489,000
Unamortized senior term note discount					4,676,000		4,676,000			$ 4,949,000
Amortization expense related to deferred debt issuance costs							1,781,000	$ 1,663,000
Maximum [Member]
Unsecured Line Of Credit And Term Notes [Line Items]
Leverage ratio percentage			60.00%
Indenture covenant percentage on unencumbered assets			150.00%
Minimum [Member]
Unsecured Line Of Credit And Term Notes [Line Items]
Interest coverage ratio on debt			150.00%
Secured Debt [Member] \| Maximum [Member]
Unsecured Line Of Credit And Term Notes [Line Items]
Leverage ratio percentage			40.00%
Revolving Credit Facility [Member]
Unsecured Line Of Credit And Term Notes [Line Items]
Revolving credit limit					$ 500,000,000		$ 500,000,000
Maturity on December 10, 2019 [Member]
Unsecured Line Of Credit And Term Notes [Line Items]
Basis spread over LIBOR							1.10%
Facility fee							0.15%
Interest rate, line of credit facility					3.19%		3.19%			2.63%
Amount available on unsecured revolving line of credit					$ 386,200,000		$ 386,200,000
Line of credit facility, expiration date							Dec. 10, 2019
Maturity on June 4, 2020 [Member]
Unsecured Line Of Credit And Term Notes [Line Items]
Basis spread over LIBOR							1.15%
Unsecured term note					325,000,000		$ 325,000,000
Repayments of unsecured term note							225,000,000
Term notes, outstanding amount					$ 100,000,000		$ 100,000,000
Debt instrument variable interest rate					3.15%		3.15%			2.53%
Maturity in April 8, 2024 [Member]
Unsecured Line Of Credit And Term Notes [Line Items]
Line of credit facility, expiration date				Apr. 08, 2024
Debt instrument stated interest rate				4.533%
Additional secured term note				$ 175,000,000
Maturity in April 8, 2024 [Member] \| Maximum [Member]
Unsecured Line Of Credit And Term Notes [Line Items]
Debt instrument stated interest rate				6.283%
Maturity in August 2021 [Member]
Unsecured Line Of Credit And Term Notes [Line Items]
Line of credit facility, expiration date									Aug. 05, 2021
Debt instrument stated interest rate									5.54%
Additional secured term note									$ 100,000,000
Maturity in August 2021 [Member] \| Maximum [Member]
Unsecured Line Of Credit And Term Notes [Line Items]
Debt instrument stated interest rate									7.29%
Senior Term Note Due July 1, 2026 [Member]
Unsecured Line Of Credit And Term Notes [Line Items]
Unsecured term note					$ 600,000,000		$ 600,000,000			$ 600,000,000
Senior Term Note Due July 1, 2026 [Member] \| Unsecured Senior Notes [Member]
Unsecured Line Of Credit And Term Notes [Line Items]
Debt instrument principal amount			$ 600,000,000		600,000,000		600,000,000
Debt instrument stated interest rate			3.50%
Debt instrument percentage discount to par			0.553%
Unamortized senior term note discount			$ 3,300,000
Underwriting discount and other offering expenses			5,500,000
Proceeds from senior notes, net			$ 591,200,000
Term Note Due July 21, 2028 [Member]
Unsecured Line Of Credit And Term Notes [Line Items]
Unsecured term note					200,000,000		200,000,000			200,000,000
Line of credit facility, expiration date		Jul. 21, 2028
Debt instrument stated interest rate		3.67%
Additional secured term note		$ 200,000,000
Senior Notes and Term Notes [Member]
Unsecured Line Of Credit And Term Notes [Line Items]
Amortization expense related to deferred debt issuance costs					500,000	$ 500,000	1,000,000	$ 1,000,000
Senior Term Note Due December 15, 2027 [Member]
Unsecured Line Of Credit And Term Notes [Line Items]
Unsecured term note					$ 450,000,000		$ 450,000,000			$ 450,000,000
Senior Term Note Due December 15, 2027 [Member] \| Unsecured Senior Notes [Member]
Unsecured Line Of Credit And Term Notes [Line Items]
Debt instrument principal amount	$ 450,000,000
Debt instrument stated interest rate	3.875%
Debt instrument percentage discount to par	0.477%
Unamortized senior term note discount	$ 2,100,000
Underwriting discount and other offering expenses	4,000,000
Proceeds from senior notes, net	$ 443,900,000