Debt instrument maturity year.

No definition available.

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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.

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- 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.

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
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-Section 45
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- Definition

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

+ References

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

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- 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

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- Definition

Description of the maturity date of the debt instrument including whether the debt matures serially and, if so, a brief description of the serial maturities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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

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- Definition

Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph e
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

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- Definition

Percentage of principal amount of debt redeemed.

+ References

No definition available.

+ Details

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- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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Period Type:	instant

- 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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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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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/presentationRef
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-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
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- Definition

Fair value portion of notes payable.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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Line of Credit, Long-Term Debt and Capital Lease Obligations - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 08, 2015
Debt Instrument [Line Items]
Line of Credit facility, maturity date	Oct. 31, 2022
Long term debt	$ 1,846,133,000	$ 1,698,744,000
Letters of credit outstanding amount	200,000
Line of Credit facility, available balance	$ 889,300,000
Minimum [Member]
Debt Instrument [Line Items]
Commitment fee percentage	0.15%
Maximum [Member]
Debt Instrument [Line Items]
Commitment fee percentage	0.30%
Alternate Base Rate [Member] \| Federal Funds Rate [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate	Federal Funds Rate plus 1/2 of 1.00%
Alternate Base Rate [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate	LIBOR for an interest period of one month plus 1.00%
Debt instrument, variable interest rate	1.00%
Applicable Margin Rate [Member] \| LIBOR [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, variable interest rate	0.125%
Applicable Margin Rate [Member] \| LIBOR [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, variable interest rate	0.75%
Unsecured Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit facility, borrowing capacity	$ 2,000,000,000
Letters of Credit [Member]
Debt Instrument [Line Items]
Line of Credit facility, borrowing capacity	$ 37,500,000
5.25% Senior Unsecured Notes Due 2023 [Member]
Debt Instrument [Line Items]
Aggregate principal amount of debt			$ 750,000,000
Debt instrument interest rate			5.25%
Debt instrument maturity date description	Payable semi-annually in arrears on June 1 and December 1
Debt instrument, maturity year	2023
Long term debt	$ 740,497,000	738,891,000
Estimated fair value of notes	$ 763,100,000	$ 773,400,000
5.25% Senior Unsecured Notes Due 2023 [Member] \| Change In Control [Member]
Debt Instrument [Line Items]
Redemption percentage of principal amount	101.00%
5.25% Senior Unsecured Notes Due 2023 [Member] \| Redemption Before 2018 [Member]
Debt Instrument [Line Items]
Redemption percentage of principal amount	100.00%
5.25% Senior Unsecured Notes Due 2023 [Member] \| Redemption Before 2018 [Member] \| Redeem up to 35% of Aggregate Principal Amount [Member]
Debt Instrument [Line Items]
Redemption percentage of principal amount	35.00%
Redemption price percentage of aggregate principal amount redeemed	105.25%
5.25% Senior Unsecured Notes Due 2023 [Member] \| Redemption in 2018 [Member]
Debt Instrument [Line Items]
Redemption percentage of principal amount	103.938%
5.25% Senior Unsecured Notes Due 2023 [Member] \| Redemption in 2019[Member]
Debt Instrument [Line Items]
Redemption percentage of principal amount	102.625%
5.25% Senior Unsecured Notes Due 2023 [Member] \| Redemption in 2020 [Member]
Debt Instrument [Line Items]
Redemption percentage of principal amount	101.313%
5.25% Senior Unsecured Notes Due 2023 [Member] \| Redemption in 2021 and Thereafter [Member]
Debt Instrument [Line Items]
Redemption percentage of principal amount	100.00%