Property and Equipment (Property and Equipment Under Capital Lease Obligations) (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Finance leases	$ 5,541	$ 5,442
Total property and equipment	167,766	163,608
Less: accumulated depreciation and amortization (including software license arrangements of $1,428 in 2020 and $400 in 2019)	(136,793)	(131,915)
Total property and equipment, net	30,973	31,693
Computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	96,657	103,604
Capitalized internal-use software
Property, Plant and Equipment [Line Items]
Property and equipment, gross	36,489	21,534
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	15,643	18,453
Computer software
Property, Plant and Equipment [Line Items]
Property and equipment, gross	9,306	8,956
Software license arrangements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,611	936
Less: accumulated depreciation and amortization (including software license arrangements of $1,428 in 2020 and $400 in 2019)	(1,428)	(400)
Office equipment, furniture, and other
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 4,130	$ 5,619