Segment and Geographic Information-Revenues and Long-lived Assets (Details) - USD ($)
$ in Thousands |
12 Months Ended |
Dec. 31, 2015 |
Dec. 31, 2014 |
Dec. 31, 2013 |
| Revenues from External Customers and Long-Lived Assets [Line Items] |
|
|
|
| Revenues before reimbursements |
$ 1,170,385
|
$ 1,142,851
|
$ 1,163,445
|
| International |
|
|
|
| Revenues from External Customers and Long-Lived Assets [Line Items] |
|
|
|
| Revenues before reimbursements |
506,650
|
488,284
|
488,488
|
| Long-lived assets |
58,442
|
21,714
|
21,288
|
| International | U.K. |
|
|
|
| Revenues from External Customers and Long-Lived Assets [Line Items] |
|
|
|
| Revenues before reimbursements |
186,375
|
128,561
|
119,747
|
| Long-lived assets |
51,457
|
12,116
|
9,691
|
| International | Canada |
|
|
|
| Revenues from External Customers and Long-Lived Assets [Line Items] |
|
|
|
| Revenues before reimbursements |
110,180
|
129,246
|
122,748
|
| Long-lived assets |
238
|
2,274
|
3,571
|
| International | Other |
|
|
|
| Revenues from External Customers and Long-Lived Assets [Line Items] |
|
|
|
| Revenues before reimbursements |
210,095
|
230,477
|
245,993
|
| Long-lived assets |
$ 6,747
|
$ 7,324
|
$ 8,026
|