Leases - Future minimum payments (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Operating lease liabilities under Topic 842
Operating leases - 2020	$ 7,334	$ 29,872
Operating leases - 2021	31,544	27,445
Operating leases - 2022	27,430	23,540
Operating leases - 2023	25,095	21,257
Operating leases - 2024	23,986	20,176
Operating leases - later years	74,358	70,842
Operating leases - Total	189,747	193,132
Less: Imputed interest	(24,789)	(27,993)
Operating lease liabilities	164,958	165,139
Finance lease liabilities under Topic 842
Finance leases - 2020	872	3,068
Finance leases - 2021	3,535	3,159
Finance leases - 2022	3,629	3,252
Finance leases - 2023	3,725	3,349
Finance leases - 2024	3,830	3,448
Finance leases - later years	13,163	8,220
Finance leases - Total	28,754	24,496
Less: imputed interest	(4,785)	(4,686)
Finance lease liabilities	$ 23,969	$ 19,810