Property and equipment - Summary by type (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Property and equipment
Total property and equipment	$ 481,671	$ 423,323
Less: accumulated depreciation and amortization	(220,661)	(172,558)
Total property and equipment, net	261,010	250,765
Leasehold improvements
Property and equipment
Total property and equipment	405,712	358,477
Software
Property and equipment
Total property and equipment	39,481	33,349
Construction in progress
Property and equipment
Total property and equipment	22,249	18,859
Computer equipment
Property and equipment
Total property and equipment	12,437	10,878
Furniture, fixtures and office equipment
Property and equipment
Total property and equipment	$ 1,792	$ 1,760