Goodwill and Intangible Assets - Intangible Assets (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Customer relationships, Gross Carrying Amount	$ 64,939	$ 68,296
Acquired technology, Gross Carrying Amount	68,977	69,200
Non-compete agreements, Gross Carrying Amount	13,665	14,632
Indefinite-lived intangible assets:
Gross Carrying Amount	196,249	201,484
Accumulated Amortization	(117,914)	(116,628)
Net Balance	78,335	84,856
Trademarks [Member]
Indefinite-lived intangible assets:
Net Balance, Indefinite-Lived Intangible Assets	44,268	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	$ (54,152)	(54,213)
Net Balance, Finite-Lived Intangible Assets	$ 10,787	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	$ (50,835)	(48,945)
Net Balance, Finite-Lived Intangible Assets	$ 18,142	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	$ (12,927)	(13,470)
Net Balance, Finite-Lived Intangible Assets	$ 738	$ 1,162