Goodwill and Intangible Assets (Schedule of Acquired Intangible Assets) (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 216,749	$ 246,779
Accumulated Amortization	(164,409)	(149,912)
Accumulated Impairment		(17,308)
Net Carrying Amount	52,340	79,559
Acquired methodologies and technology
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	148,403	148,386
Accumulated Amortization	(106,771)	(86,771)
Accumulated Impairment		0
Net Carrying Amount	41,632	61,615
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	40,168	40,143
Accumulated Amortization	(31,170)	(25,864)
Accumulated Impairment		0
Net Carrying Amount	8,998	14,279
Intellectual property
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	14,379	14,372
Accumulated Amortization	(12,787)	(12,346)
Accumulated Impairment		0
Net Carrying Amount	1,592	2,026
Acquired software
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	9,287	9,287
Accumulated Amortization	(9,286)	(7,928)
Accumulated Impairment		0
Net Carrying Amount	1	1,359
Panel
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	3,139	3,123
Accumulated Amortization	(3,139)	(3,123)
Accumulated Impairment		0
Net Carrying Amount	0	0
Trade Names
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	773	768
Accumulated Amortization	(757)	(691)
Accumulated Impairment		0
Net Carrying Amount	16	77
Strategic alliance
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	0	30,100
Accumulated Amortization	0	(12,792)
Accumulated Impairment		(17,308)
Net Carrying Amount	0	0
Other
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	600	600
Accumulated Amortization	(499)	(397)
Accumulated Impairment		0
Net Carrying Amount	$ 101	$ 203