Property and equipment - Summary by type (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Property and equipment
Total property and equipment	$ 461,140	$ 423,323
Less: accumulated depreciation and amortization	(202,396)	(172,558)
Total property and equipment, net	258,744	250,765
Leasehold improvements
Property and equipment
Total property and equipment	378,194	358,477
Software
Property and equipment
Total property and equipment	37,180	33,349
Construction in progress
Property and equipment
Total property and equipment	31,998	18,859
Computer equipment
Property and equipment
Total property and equipment	12,017	10,878
Furniture, fixtures and office equipment
Property and equipment
Total property and equipment	$ 1,751	$ 1,760