Fair value of financial instruments - Schedule of Financial Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Fair value measurements on a recurring basis:
Derivative financial instruments	$ 40,811	$ 46,340
Fair Value Measurements on a Recurring Basis | Interest rate swap
Fair value measurements on a recurring basis:
Derivative financial instruments	40,811	46,340
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	40,811	46,340
Fair Value Measurements on a Recurring Basis | Level 3 | Interest rate swap
Fair value measurements on a recurring basis:
Derivative financial instruments	$ 0	$ 0