Schedule of Amortizable Intangible Assets (Detail) - USD ($) $ in Thousands		9 Months Ended	12 Months Ended
		Sep. 30, 2018	Dec. 31, 2017
Goodwill and Other Intangible Assets [Line Items]
Cost		$ 127,439	$ 127,467
Accumulated Amortization		(104,061)	(95,568)
Net Book Value	[1]	23,378	31,899
Client related intangibles
Goodwill and Other Intangible Assets [Line Items]
Cost		63,136	63,164
Accumulated Amortization		(49,633)	(44,835)
Net Book Value	[1]	$ 13,503	$ 18,329
Client related intangibles | Minimum
Goodwill and Other Intangible Assets [Line Items]
Useful Lives		4 years	4 years
Client related intangibles | Maximum
Goodwill and Other Intangible Assets [Line Items]
Useful Lives		10 years	10 years
Technology
Goodwill and Other Intangible Assets [Line Items]
Cost		$ 58,942	$ 58,942
Accumulated Amortization		(49,067)	(45,372)
Net Book Value	[1]	$ 9,875	$ 13,570
Technology | Minimum
Goodwill and Other Intangible Assets [Line Items]
Useful Lives		3 years	3 years
Technology | Maximum
Goodwill and Other Intangible Assets [Line Items]
Useful Lives		10 years	10 years
Other intangibles
Goodwill and Other Intangible Assets [Line Items]
Cost		$ 5,361	$ 5,361
Accumulated Amortization		$ (5,361)	$ (5,361)
Other intangibles | Minimum
Goodwill and Other Intangible Assets [Line Items]
Useful Lives		1 year	1 year
Other intangibles | Maximum
Goodwill and Other Intangible Assets [Line Items]
Useful Lives		5 years	5 years

[1] Included in other long-term assets.