Leases - Future minimum payments (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Operating lease liabilities under Topic 842
Operating leases - 2020	$ 15,955	$ 29,872
Operating leases - 2021	30,619	27,445
Operating leases - 2022	26,527	23,540
Operating leases - 2023	24,225	21,257
Operating leases - 2024	23,130	20,176
Operating leases - later years	73,346	70,842
Operating leases - Total	193,802	193,132
Less: Imputed interest	(25,851)	(27,993)
Operating lease liabilities	167,951	165,139
Finance lease liabilities under Topic 842
Finance leases - 2020	1,613	3,068
Finance leases - 2021	3,299	3,159
Finance leases - 2022	3,392	3,252
Finance leases - 2023	3,489	3,349
Finance leases - 2024	3,594	3,448
Finance leases - later years	8,938	8,220
Finance leases - Total	24,325	24,496
Less: imputed interest	(4,305)	(4,686)
Finance lease liabilities	$ 20,020	$ 19,810