Operating Segment and Enterprise Wide Reporting - Schedule of Information about Reportable Segments (Detail) - USD ($) $ in Thousands |
3 Months Ended | 12 Months Ended | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Dec. 31, 2016 |
Sep. 30, 2016 |
Jun. 30, 2016 |
Mar. 31, 2016 |
Dec. 31, 2015 |
Sep. 30, 2015 |
Jun. 30, 2015 |
Mar. 31, 2015 |
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
|
| Segment Reporting Information [Line Items] | |||||||||||
| Research services revenues | $ 215,216 | $ 210,268 | $ 207,517 | ||||||||
| Advisory services and events revenues | 110,879 | 103,458 | 104,545 | ||||||||
| Total revenues | $ 83,446 | $ 77,427 | $ 87,821 | $ 77,401 | $ 80,975 | $ 74,753 | $ 82,811 | $ 75,187 | 326,095 | 313,726 | 312,062 |
| Segment expenses | 119,307 | 117,445 | 120,009 | ||||||||
| Contribution margin (loss) | 206,788 | 196,281 | 192,053 | ||||||||
| Selling, marketing, administrative and other expenses | (174,157) | (172,130) | (169,852) | ||||||||
| Amortization of intangible assets | (831) | (891) | (2,171) | ||||||||
| Reorganization costs | (1,026) | (4,433) | (1,817) | ||||||||
| Other income and losses on investments | (65) | 493 | 176 | ||||||||
| Income before income taxes | 30,709 | 19,320 | 18,389 | ||||||||
| Product Segment [Member] | |||||||||||
| Segment Reporting Information [Line Items] | |||||||||||
| Research services revenues | 215,216 | 210,268 | 207,517 | ||||||||
| Advisory services and events revenues | 20,374 | 17,512 | 20,759 | ||||||||
| Total revenues | 235,590 | 227,780 | 228,276 | ||||||||
| Segment expenses | 41,528 | 38,615 | 39,466 | ||||||||
| Contribution margin (loss) | 194,062 | 189,165 | 188,810 | ||||||||
| Research Segment [Member] | |||||||||||
| Segment Reporting Information [Line Items] | |||||||||||
| Advisory services and events revenues | 45,601 | 42,997 | 48,658 | ||||||||
| Total revenues | 45,601 | 42,997 | 48,658 | ||||||||
| Segment expenses | 51,132 | 51,510 | 53,307 | ||||||||
| Contribution margin (loss) | (5,531) | (8,513) | (4,649) | ||||||||
| Project Consulting [Member] | |||||||||||
| Segment Reporting Information [Line Items] | |||||||||||
| Advisory services and events revenues | 44,904 | 42,949 | 35,128 | ||||||||
| Total revenues | 44,904 | 42,949 | 35,128 | ||||||||
| Segment expenses | 26,647 | 27,320 | 27,236 | ||||||||
| Contribution margin (loss) | $ 18,257 | $ 15,629 | $ 7,892 | ||||||||