Leases - Office and equipment leases (Details) $ in Thousands	Dec. 31, 2019 USD ($)
Future minimum payments for operating lease liabilities
2020	$ 622,056
2021	554,000
2022	542,952
2023	538,771
2024	530,003
Thereafter	1,851,738
Total lease payments	4,639,520
Less: imputed interest	(1,753,020)
Total lease liabilities, operating leases	2,886,500
Office and Equipment Leases
Future minimum payments for operating lease liabilities
2020	10,061
2021	9,002
2022	7,232
2023	4,803
2024	4,792
Thereafter	27,258
Total lease payments	63,148
Less: imputed interest	(15,009)
Total lease liabilities, operating leases	48,139
Office Leases
Future minimum payments for operating lease liabilities
2020	6,145
2021	6,071
2022	6,027
2023	4,761
2024	4,792
Thereafter	27,258
Total lease payments	55,054
Less: imputed interest	(14,562)
Total lease liabilities, operating leases	40,492
Equipment Leases
Future minimum payments for operating lease liabilities
2020	3,916
2021	2,931
2022	1,205
2023	42
Total lease payments	8,094
Less: imputed interest	(447)
Total lease liabilities, operating leases	$ 7,647