Property and equipment (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Property and equipment
Total property and equipment	$ 255,492	$ 198,764
Less: accumulated depreciation and amortization	(103,486)	(86,992)
Total property and equipment, net	152,006	111,772
Leasehold improvements
Property and equipment
Total property and equipment	179,401	152,627
Construction in progress
Property and equipment
Total property and equipment	42,814	20,104
Computer equipment
Property and equipment
Total property and equipment	10,698	7,909
Software
Property and equipment
Total property and equipment	20,840	17,827
Office equipment
Property and equipment
Total property and equipment	$ 1,739	$ 297