Debt - Interest Rate Swaps (Details) - Cash flow hedging - Designated as hedging instrument - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Interest rate swaps
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional value	$ 1,630,000	$ 1,630,000
Interest rate swap - January 2020 - 1
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	1.63%
Notional value	$ 0	50,000
Interest rate swap - January 2020 - 2
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	1.63%
Notional value	$ 0	50,000
Interest rate swap - January 2020 - 3
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	2.46%
Notional value	$ 0	50,000
Interest rate swap - January 2020 - 4
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	2.46%
Notional value	$ 0	50,000
Interest rate swap - January 2020 - 5
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	1.66%
Notional value	$ 0	50,000
Interest rate swap - January 2020 - 6
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	1.66%
Notional value	$ 0	50,000
Interest rate swap - December 2020 - 1
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	2.12%
Notional value	$ 100,000	100,000
Interest rate swap - December 2020 - 2
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	2.12%
Notional value	$ 100,000	100,000
Interest rate swap - January 2021 - 1
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	1.74%
Notional value	$ 75,000	75,000
Interest rate swap - January 2021 - 2
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	1.75%
Notional value	$ 50,000	50,000
Interest rate swap - January 2021 - 3
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	1.53%
Notional value	$ 37,500	37,500
Interest rate swap - January 2021 - 4
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	1.53%
Notional value	$ 37,500	37,500
Interest rate swap - January 2021 - 5
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	1.46%
Notional value	$ 100,000	100,000
Interest rate swap - January 2021 - 6
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	1.47%
Notional value	$ 47,500	47,500
Interest rate swap - January 2021 - 7
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	1.47%
Notional value	$ 47,500	47,500
Interest rate swap - January 2021 - 8
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	1.47%
Notional value	$ 47,500	47,500
Interest rate swap - January 2021 - 9
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	1.47%
Notional value	$ 47,500	47,500
Interest rate swap - October 2021 - 1
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	2.60%
Notional value	$ 55,000	55,000
Interest rate swap - October 2021 - 2
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	2.60%
Notional value	$ 55,000	55,000
Interest rate swap - January 2022 - 1
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	1.78%
Notional value	$ 100,000	100,000
Interest rate swap - January 2022 - 2
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	1.78%
Notional value	$ 50,000	50,000
Interest rate swap - January 2022 - 3
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	1.79%
Notional value	$ 30,000	30,000
Interest rate swap - April 2022 - 1
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	1.68%
Notional value	$ 25,000	25,000
Interest rate swap - April 2022 - 2
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	1.68%
Notional value	$ 25,000	25,000
Interest rate swap - April 2022 - 3
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	1.64%
Notional value	$ 25,000	25,000
Interest rate swap - April 2022 - 4
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	1.64%
Notional value	$ 25,000	25,000
Interest rate swap - November 2023 - 1
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	1.99%
Notional value	$ 85,000	85,000
Interest rate swap - November 2023 - 2
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	1.99%
Notional value	$ 85,000	85,000
Interest rate swap - November 2023 - 3
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	1.99%
Notional value	$ 50,000	50,000
Interest rate swap - November 2023 - 4
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	1.99%
Notional value	$ 30,000	30,000
Interest rate swap - January 2024 - 1
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	2.60%
Notional value	$ 75,000	0
Interest rate swap - January 2024 - 2
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	2.60%
Notional value	$ 50,000	0
Interest rate swap - January 2024 - 3
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	2.60%
Notional value	$ 25,000	0
Interest rate swap - January 2024 - 4
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	2.60%
Notional value	$ 75,000	0
Interest rate swap - January 2024 - 5
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Interest rate	2.60%
Notional value	$ 75,000	$ 0