Accumulated other comprehensive loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Increase (Decrease) Accumulated Other Comprehensive Income (Loss) Net of Tax [Roll Forward]
Balance as of December 31, 2018	$ (10,435)
Unrealized interest rate hedge (losses) gains arising during the period	(1,763)	$ 1,622	$ 2,837
Unrealized foreign currency translation gains (losses) arising during the period	2,524	(7,369)	7,774
Other comprehensive income (loss) before reclassifications	761
Reclassification adjustment for amortization (income) expense to interest expense included in net income	(1,777)	(4,941)	1,915
Reclassification adjustment for cumulative foreign currency translation losses included in net income (loss) upon sale or liquidation	0	0	1,599
Amounts reclassified from other comprehensive income	(1,777)
Reclassification of losses related to terminated interest rate hedge instruments to interest expense included in net (loss) income	1,702	0	$ 0
Reclassification of losses in accumulated other comprehensive income (loss) to interest expense upon swap termination	1,702
Net other comprehensive (loss) income	686
Balance as of December 31, 2019	(9,749)	(10,435)
Interest rate hedge agreements
Increase (Decrease) Accumulated Other Comprehensive Income (Loss) Net of Tax [Roll Forward]
Balance as of December 31, 2018	1,838
Net other comprehensive (loss) income	(1,838)
Balance as of December 31, 2019	0	1,838
Foreign currency translation
Increase (Decrease) Accumulated Other Comprehensive Income (Loss) Net of Tax [Roll Forward]
Balance as of December 31, 2018	(12,273)
Net other comprehensive (loss) income	2,524
Balance as of December 31, 2019	$ (9,749)	$ (12,273)