Property and equipment - Summary by type (Details) - USD ($) $ in Thousands |
Sep. 30, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Property and equipment | ||
| Total property and equipment | $ 544,986 | $ 502,646 |
| Less: accumulated depreciation and amortization | (247,056) | (240,287) |
| Total property and equipment, net | 297,930 | 262,359 |
| Leasehold improvements | ||
| Property and equipment | ||
| Total property and equipment | 433,130 | 418,023 |
| Software | ||
| Property and equipment | ||
| Total property and equipment | 49,675 | 42,281 |
| Construction in progress | ||
| Property and equipment | ||
| Total property and equipment | 46,649 | 27,291 |
| Computer equipment | ||
| Property and equipment | ||
| Total property and equipment | 13,666 | 13,245 |
| Furniture, fixtures and office equipment | ||
| Property and equipment | ||
| Total property and equipment | $ 1,866 | $ 1,806 |