Fair value of the assets less the liabilities of a derivative or group of derivatives.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13433-108611

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- Definition

Fixed interest rate related to the interest rate derivative.

+ References

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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.

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

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- Definition

Nominal or face amount used to calculate payment on derivative.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
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-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5579245-113959

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Amount, after tax, of reclassification of gain (loss) from accumulated other comprehensive income (AOCI) for derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=118930883&loc=d3e689-108580

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Topic 220
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-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=118930883&loc=d3e637-108580

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Derivative Instruments - Interest rate derivatives and their fair values (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Apr. 05, 2017
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Reclassification of other comprehensive income to interest expense		$ (1,000)	$ 100	$ 0
Forecast
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Reclassification of other comprehensive income to interest expense	$ (3,600)
Interest Rate Swap
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount of derivative					$ 400,000
Interest Rate Swap \| Cash flow hedging
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Fair value		(19,916)	2,343
Swap instrument one matures on December 17, 2021 \| Cash flow hedging
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount of derivative		$ 25,000	25,000
Fixed Rate Per annum		1.989%
Expiration Date		Dec. 17, 2021
Fair value		$ (209)	331
Swap instrument two matures on December 17, 2021 \| Cash flow hedging
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount of derivative		$ 100,000	100,000
Fixed Rate Per annum		1.989%
Expiration Date		Dec. 17, 2021
Fair value		$ (837)	1,318
Swap instrument three matures on December 17, 2021 \| Cash flow hedging
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount of derivative		$ 75,000	75,000
Fixed Rate Per annum		1.989%
Expiration Date		Dec. 17, 2021
Fair value		$ (627)	990
Swap instrument one matures on April 27, 2022 \| Cash flow hedging
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount of derivative		$ 50,000	50,000
Fixed Rate Per annum		2.033%
Expiration Date		Apr. 27, 2022
Fair value		$ (545)	667
Swap instrument two matures on April 27, 2022 \| Cash flow hedging
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount of derivative		$ 100,000	100,000
Fixed Rate Per annum		2.029%
Expiration Date		Apr. 27, 2022
Fair value		$ (1,081)	1,341
Swap instrument three matures on April 27, 2022 \| Cash flow hedging
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount of derivative		$ 50,000	50,000
Fixed Rate Per annum		2.033%
Expiration Date		Apr. 27, 2022
Fair value		$ (545)	666
Swap instrument one matures on December 17, 2023 \| Cash flow hedging
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount of derivative		$ 100,000	100,000
Fixed Rate Per annum		2.617%
Expiration Date		Dec. 17, 2023
Fair value		$ (4,007)	(782)
Swap instrument one matures on April 27, 2024 \| Cash flow hedging
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount of derivative		$ 100,000	100,000
Fixed Rate Per annum		2.621%
Expiration Date		Apr. 27, 2024
Fair value		$ (4,324)	(818)
Swap instrument two matures on December 17, 2023
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount of derivative		$ 200,000	200,000
Fixed Rate Per annum		2.636%
Expiration Date		Dec. 17, 2023
Fair value		$ (3,939)	(722)
Swap instrument two matures on April 27, 2024 \| Cash flow hedging
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount of derivative		$ 200,000	200,000
Fixed Rate Per annum		2.642%
Expiration Date		Apr. 27, 2024
Fair value		$ (3,802)	$ (648)