Acquisitions - Narrative (Detail) - USD ($) $ in Thousands							12 Months Ended
	Nov. 29, 2017	Aug. 02, 2017	May 30, 2017	May 31, 2016	Nov. 16, 2015	May 29, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Payments to acquire business, net of cash acquired							$ 11,344	$ 9,394	$ 339,961
Radio 1033, LLC
Business Acquisition [Line Items]
Total purchase price to acquire business	$ 1,400
Digital Health Department, Inc.
Business Acquisition [Line Items]
Total purchase price to acquire business		$ 3,900
Modria.com
Business Acquisition [Line Items]
Total purchase price to acquire business			$ 7,000
Cash to acquire business			$ 6,100
Accrued amount from business acquisition							$ 900
ExecuTime Software, LLC
Business Acquisition [Line Items]
Total purchase price to acquire business				$ 7,400
New World Systems Corporation
Business Acquisition [Line Items]
Cash acquired from acquisition					$ 22,500
Payments to acquire business, net of cash acquired					$ 337,500
Accrued purchase price								4,000	$ 4,000
Number of shares of equity interests issued to acquire entity					2,100,000
Value of shares of equity interests issued to acquire entity					$ 362,800
Acquisition related fees					$ 5,900
Payment for previous acquisition								2,000
Goodwill, purchase price adjustments								$ 7,400
Brazos Technology Corporation
Business Acquisition [Line Items]
Cash acquired from acquisition						$ 312
Payments to acquire business, net of cash acquired						$ 6,100
Number of shares of equity interests issued to acquire entity						12,500
Value of shares of equity interests issued to acquire entity						$ 1,500
Debt assumed in acquisition						$ 733