Capitalized Software Development Costs - Summary of Capitalized Software Development Costs (Detail) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Capitalized Computer Software Net [Line Items]
Gross carrying amount	$ 41,141	$ 36,899
Accumulated amortization	(29,654)	(26,894)
Net carrying amount	11,487	10,005
Capitalized software development costs [Member]
Capitalized Computer Software Net [Line Items]
Gross carrying amount	$ 41,141	$ 36,899
Amortization period	3 years	3 years
Accumulated amortization	$ (29,654)	$ (26,894)
Net carrying amount	$ 11,487	$ 10,005