Intangible Assets - Intangible Assets (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Customer relationships, Gross Carrying Amount	$ 68,479	$ 68,296
Acquired technology, Gross Carrying Amount	69,443	69,200
Non-compete agreements, Gross Carrying Amount	14,678	14,632
Indefinite-lived intangible assets:
Gross Carrying Amount	202,339	201,484
Accumulated Amortization	(118,836)	(116,628)
Net Balance	83,503	84,856
Trademarks [Member]
Indefinite-lived intangible assets:
Net Balance, Indefinite-Lived Intangible Assets	45,339	44,956
Domain Names [Member]
Indefinite-lived intangible assets:
Net Balance, Indefinite-Lived Intangible Assets	$ 4,400	4,400
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, Weighted-Average Amortization Period (Years)	10 years
Indefinite-lived intangible assets:
Accumulated Amortization	$ (55,068)	(54,213)
Net Balance, Finite-Lived Intangible Assets	$ 13,411	14,083
Acquired Technology [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, Weighted-Average Amortization Period (Years)	11 years
Indefinite-lived intangible assets:
Accumulated Amortization	$ (50,107)	(48,945)
Net Balance, Finite-Lived Intangible Assets	$ 19,336	20,255
Non-compete Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, Weighted-Average Amortization Period (Years)	4 years
Indefinite-lived intangible assets:
Accumulated Amortization	$ (13,661)	(13,470)
Net Balance, Finite-Lived Intangible Assets	$ 1,017	$ 1,162