Revenue - Contract Balances and Transaction Price Allocated to the Remaining Performance Obligation (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Accounts Receivable
Accounts Receivables - Opening	$ 333,858	$ 331,295
Accounts Receivables - Closing	343,177	343,113
(Increase)/decrease	(9,319)	(11,818)
Current portion of deferred revenues
Current portion of deferred revenues - Opening	407,325	391,102
Current portion of deferred revenues - Closing	472,101	461,928
(Increase)/decrease	(64,776)	(70,826)
Non-current portion of deferred revenues
Non-current portion of deferred revenues - Opening	19,723	17,112
Non-current portion of deferred revenues - Closing	18,774	17,987
(Increase)/decrease	949	$ (875)
Revenue recognized	$ 105,150