Property and equipment (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Property and equipment
Total property and equipment	$ 109,626		$ 109,626		$ 93,837
Less: accumulated depreciation and amortization	(59,090)		(59,090)		(51,426)
Total property and equipment, net	50,536		50,536		42,411
Depreciation and amortization allocation
Total depreciation and amortization of property and equipment	4,734	3,358	8,867	7,873
Network access
Depreciation and amortization allocation
Total depreciation and amortization of property and equipment	3,205	2,479	6,082	6,144
Network operations
Depreciation and amortization allocation
Total depreciation and amortization of property and equipment	1,008	716	1,816	1,390
Development and technology
Depreciation and amortization allocation
Total depreciation and amortization of property and equipment	472	130	888	280
General and administrative
Depreciation and amortization allocation
Total depreciation and amortization of property and equipment	49	33	81	59
Leasehold improvements
Property and equipment
Total property and equipment	82,658		82,658		72,119
Construction in progress
Property and equipment
Total property and equipment	10,665		10,665		6,295
Computer equipment
Property and equipment
Total property and equipment	7,230		7,230		7,493
Software
Property and equipment
Total property and equipment	8,662		8,662		7,519
Office equipment
Property and equipment
Total property and equipment	$ 411		$ 411		$ 411