Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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- Definition

The percentage points added to the reference rate to compute the variable rate on the interest rate derivative.

+ References

No definition available.

+ Details

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- Definition

Fixed interest rate related to the interest rate derivative.

+ References

No definition available.

+ Details

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- Definition

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

+ References

No definition available.

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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

Fair value as of the balance sheet date of interest rate derivative assets, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13433-108611

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- Definition

Fair value as of the balance sheet date of interest rate derivative liabilities, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as liabilities.

+ References

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- Definition

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 set, unchanging rate.

+ References

No definition available.

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- Definition

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

No definition available.

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- Definition

Number of interest rate derivative instruments held by the entity at the reporting date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5579245-113959

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Derivative Instruments and Hedging Activities (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) interest_rate_swap
Derivatives, Fair Value [Line Items]
Number of interest rate swaps \| interest_rate_swap			2
Long-term debt, percentage bearing fixed interest, amount	$ 200,000
Long-term debt, percentage bearing variable interest, amount	44,000
5 year interest rate swap
Derivatives, Fair Value [Line Items]
Notional amount	$ 25,000
Fixed interest rate	2.50%
Maturity date	Aug. 29, 2024
Interest rate derivative assets	$ 205
Interest rate derivative liabilities		$ (492)
10 year interest rate swap
Derivatives, Fair Value [Line Items]
Notional amount	$ 25,000
Fixed interest rate	1.73%
Maturity date	Aug. 29, 2019
Interest rate derivative assets	$ 344
Interest Rate Swap
Derivatives, Fair Value [Line Items]
Notional amount			$ 50,000
Interest rate derivative assets	549
Interest rate derivative liabilities		(422)
Other Noncurrent Liabilities [Member] \| Level 2 \| 10 year interest rate swap
Derivatives, Fair Value [Line Items]
Interest rate derivative liabilities		(492)
Other Assets [Member] \| Level 2 \| 5 year interest rate swap
Derivatives, Fair Value [Line Items]
Interest rate derivative assets	205	$ 70
Other Assets [Member] \| Level 2 \| 10 year interest rate swap
Derivatives, Fair Value [Line Items]
Interest rate derivative assets	$ 344
London Interbank Offered Rate (LIBOR) [Member] \| Minimum
Derivatives, Fair Value [Line Items]
Derivative, basis spread on variable rate	1.38%
London Interbank Offered Rate (LIBOR) [Member] \| Maximum
Derivatives, Fair Value [Line Items]
Derivative, basis spread on variable rate	2.00%