Business Acquisitions and Divestitures - Schedule of Recognized Identified Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 27, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Identifiable intangibles	$ 85,000
Goodwill	8,820,313	$ 8,647,142		$ 5,824,726
Deltek
Business Acquisition [Line Items]
Accounts receivable			$ 94,506
Other current assets			37,558
Identifiable intangibles	$ 972,000		972,000
Goodwill			2,234,549
Other assets			43,098
Total assets acquired			3,381,711
Deferred revenue			166,393
Other current liabilities			57,433
Long-term deferred tax liability			349,810
Other liabilities			7,935
Net assets acquired			$ 2,800,140