Acquisitions - Schedule of Assets and Liabilities Acquired (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Goodwill	$ 1,802,670	$ 1,614,494	$ 1,585,893
Sapho, Inc.
Business Acquisition [Line Items]
Current assets	4,671
Intangible assets	53,600
Goodwill	144,173
Deferred taxes	0
Other assets	0
Assets acquired	202,444
Other current liabilities assumed	3,323
Assumed debt	0
Other long term liabilities assumed	370
Deferred taxes	12,094
Net assets acquired	$ 186,657
Weighted average useful life	5 years
Cedexis, Inc.
Business Acquisition [Line Items]
Current assets	$ 8,961
Intangible assets	27,200
Goodwill	44,003
Deferred taxes	3,173
Other assets	69
Assets acquired	83,406
Other current liabilities assumed	5,711
Assumed debt	5,674
Other long term liabilities assumed	0
Deferred taxes	0
Net assets acquired	$ 72,021
Minimum | Cedexis, Inc.
Business Acquisition [Line Items]
Weighted average useful life	1 year
Maximum | Cedexis, Inc.
Business Acquisition [Line Items]
Weighted average useful life	6 years