Property and equipment (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Property and equipment
Total property and equipment	$ 115,656		$ 115,656		$ 93,837
Less: accumulated depreciation and amortization	(61,051)		(61,051)		(51,426)
Total property and equipment, net	54,605		54,605		42,411
Depreciation and amortization allocation
Total depreciation and amortization of property and equipment	4,744	3,798	13,611	11,672
Network access
Depreciation and amortization allocation
Total depreciation and amortization of property and equipment	3,058	2,704	9,140	8,848
Network operations
Depreciation and amortization allocation
Total depreciation and amortization of property and equipment	1,116	687	2,932	2,077
Development and technology
Depreciation and amortization allocation
Total depreciation and amortization of property and equipment	507	375	1,395	656
General and administrative
Depreciation and amortization allocation
Total depreciation and amortization of property and equipment	63	32	144	91
Leasehold improvements
Property and equipment
Total property and equipment	85,516		85,516		72,119
Construction in progress
Property and equipment
Total property and equipment	12,599		12,599		6,295
Computer equipment
Property and equipment
Total property and equipment	7,280		7,280		7,493
Software
Property and equipment
Total property and equipment	9,848		9,848		7,519
Office equipment
Property and equipment
Total property and equipment	$ 413		$ 413		$ 411