Summary of Gross Carrying Amount and Accumulated Amortization for Intangible Assets Resulting from Acquisitions (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Acquired Finite Lived Intangible Assets [Line Items]
Gross carrying amount	$ 21,539	$ 15,239
Accumulated amortization	(12,384)	(10,874)
Intangible assets, net	$ 9,155	4,365
Minimum
Acquired Finite Lived Intangible Assets [Line Items]
Amortization period (in years)	4 years
Maximum
Acquired Finite Lived Intangible Assets [Line Items]
Amortization period (in years)	12 years
Trademarks
Acquired Finite Lived Intangible Assets [Line Items]
Amortization period (in years)	5 years
Gross carrying amount	$ 400
Accumulated amortization	(50)
Intangible assets, net	350
Developed Technology
Acquired Finite Lived Intangible Assets [Line Items]
Gross carrying amount	7,600	4,600
Accumulated amortization	(3,779)	(3,257)
Intangible assets, net	$ 3,821	1,343
Developed Technology | Minimum
Acquired Finite Lived Intangible Assets [Line Items]
Amortization period (in years)	10 years
Developed Technology | Maximum
Acquired Finite Lived Intangible Assets [Line Items]
Amortization period (in years)	12 years
Customer Relationships
Acquired Finite Lived Intangible Assets [Line Items]
Gross carrying amount	$ 13,539	10,639
Accumulated amortization	(8,555)	(7,617)
Intangible assets, net	$ 4,984	$ 3,022
Customer Relationships | Minimum
Acquired Finite Lived Intangible Assets [Line Items]
Amortization period (in years)	4 years
Customer Relationships | Maximum
Acquired Finite Lived Intangible Assets [Line Items]
Amortization period (in years)	12 years