Property and equipment - Summary by type (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Property and equipment
Total property and equipment	$ 438,466	$ 423,323
Less: accumulated depreciation and amortization	(187,531)	(172,558)
Total property and equipment, net	250,935	250,765
Leasehold improvements
Property and equipment
Total property and equipment	362,314	358,477
Software
Property and equipment
Total property and equipment	35,778	33,349
Construction in progress
Property and equipment
Total property and equipment	27,437	18,859
Computer equipment
Property and equipment
Total property and equipment	11,186	10,878
Furniture, fixtures and office equipment
Property and equipment
Total property and equipment	$ 1,751	$ 1,760