Acquisitions (Narrative) (Details) - USD ($) $ in Thousands				9 Months Ended
	Nov. 01, 2018	Feb. 06, 2018	Jan. 03, 2017	Sep. 30, 2018	Sep. 30, 2017
Finite-Lived Intangible Assets [Line Items]
Cash paid for acquisitions, net of cash acquired				$ 65,983	$ 60,449
Cedexis, Inc. [Member]
Finite-Lived Intangible Assets [Line Items]
Cash paid for acquisitions, net of cash acquired		$ 66,000
Cash acquired in business combination		$ 6,000
Unidesk Corporation [Member]
Finite-Lived Intangible Assets [Line Items]
Cash paid for acquisitions, net of cash acquired			$ 60,400
Cash acquired in business combination			$ 2,700
Subsequent Event [Member]
Finite-Lived Intangible Assets [Line Items]
Cash paid for acquisitions, net of cash acquired	$ 200,000