Fixed Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Property Plant And Equipment [Line Items]
Fixed assets, gross	$ 401,116	$ 380,694
Less: Accumulated depreciation and amortization	(279,203)	(245,277)
Fixed assets, net	121,913	135,417
Computer Equipment and Software [Member]
Property Plant And Equipment [Line Items]
Fixed assets, gross	$ 332,826	316,537
Computer Equipment and Software [Member] | Minimum [Member]
Property Plant And Equipment [Line Items]
Estimated useful life (in years)	3 years
Computer Equipment and Software [Member] | Maximum [Member]
Property Plant And Equipment [Line Items]
Estimated useful life (in years)	10 years
Facility Furniture, Fixtures and Equipment [Member]
Property Plant And Equipment [Line Items]
Fixed assets, gross	$ 21,300	23,923
Facility Furniture, Fixtures and Equipment [Member] | Minimum [Member]
Property Plant And Equipment [Line Items]
Estimated useful life (in years)	5 years
Facility Furniture, Fixtures and Equipment [Member] | Maximum [Member]
Property Plant And Equipment [Line Items]
Estimated useful life (in years)	7 years
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Fixed assets, gross	$ 37,555	33,031
Estimated useful life (in years)	Shorter of 7 years or life of lease
Assets Under Capital Leases [Member]
Property Plant And Equipment [Line Items]
Fixed assets, gross	$ 9,435	7,203
Less: Accumulated depreciation and amortization	$ (7,300)	$ (5,800)
Assets Under Capital Leases [Member] | Minimum [Member]
Property Plant And Equipment [Line Items]
Estimated useful life (in years)	3 years
Assets Under Capital Leases [Member] | Maximum [Member]
Property Plant And Equipment [Line Items]
Estimated useful life (in years)	5 years