Revenue - Contract balances (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Contract assets, net	$ 220,760		$ 220,760		$ 221,288
Increase (decrease) in unbilled receivables			(500)
Billing for the reporting period			(1,272,000)
Revenue recognized but unbilled			1,271,000
Increase or decrease in deferred revenue			(72,000)
Revenue recognized			118,000
Deferrals of customer payments			(46,000)
Capitalized Contract Cost, Amortization	$ (1,500)	$ 1,900	$ (5,300)	$ 6,200