Revenue - Contract Balances and Transaction Price Allocated to the Remaining Performance Obligation (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Accounts Receivable
Accounts Receivables - Opening	$ 333,858	$ 331,295
Accounts Receivables - Closing	279,160	270,584
(Increase)/decrease	54,698	60,711
Current portion of deferred revenues
Current portion of deferred revenues - Opening	407,325	391,102
Current portion of deferred revenues - Closing	424,187	404,753
(Increase)/decrease	(16,862)	(13,651)
Non-current portion of deferred revenues
Non-current portion of deferred revenues - Opening	19,723	17,112
Non-current portion of deferred revenues - Closing	19,116	22,236
(Increase)/decrease	607	$ (5,124)
Revenue recognized	$ 181,146