Capitalized Software Development Costs, Write Offs Included in Asset Impairment Changes and Amortization of Capitalized Software Development Costs Included in Cost of Revenue (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Capitalized software development costs	$ 115,394	$ 126,003	$ 46,464
Write-offs of capitalized software development costs	0	4,625	0
Amortization of capitalized software development costs	$ 57,084	$ 43,274	$ 46,842