Segment Information (Subscription Revenues) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017
Segment Reporting Information [Line Items]
Revenues	$ 809,823	$ 732,901	$ 748,697	$ 719,143	$ 801,870	$ 732,476	$ 742,365	$ 697,192	$ 3,010,564	$ 2,973,903	[1],[2]	$ 2,824,686	[1],[2]
Subscription
Segment Reporting Information [Line Items]
Revenues									650,810	455,276		314,735	[3]
Subscription, SaaS
Segment Reporting Information [Line Items]
Revenues									390,774	273,771		175,762	[3]
Subscription, Non-SaaS
Segment Reporting Information [Line Items]
Revenues									$ 260,036	$ 181,505		$ 138,973	[3]

[1] As noted above, prior period amounts have not been adjusted under the modified retrospective method of adoption of the revenue recognition standard.

[2] Prior period amounts have not been adjusted under the modified retrospective method of adoption of the revenue recognition standard.

[3] As noted above, prior period amounts have not been adjusted under the modified retrospective method of adoption of the revenue recognition standar