Fair value of financial instruments - Schedule of Financial Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair value measurements on a recurring basis:
Derivative financial instruments	$ 50,832	$ 31,932
Fair Value Measurements on a Recurring Basis | Interest rate swap
Fair value measurements on a recurring basis:
Derivative financial instruments	50,832	31,932
Fair Value Measurements on a Recurring Basis | Level 1 | Interest rate swap
Fair value measurements on a recurring basis:
Derivative financial instruments	0	0
Fair Value Measurements on a Recurring Basis | Level 2 | Interest rate swap
Fair value measurements on a recurring basis:
Derivative financial instruments	50,832	31,932
Fair Value Measurements on a Recurring Basis | Level 3 | Interest rate swap
Fair value measurements on a recurring basis:
Derivative financial instruments	$ 0	$ 0