Property and equipment (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Property and equipment
Total property and equipment	$ 104,376		$ 93,837
Less: accumulated depreciation and amortization	(55,363)		(51,426)
Total property and equipment, net	49,013		42,411
Depreciation and amortization allocation
Total depreciation and amortization of property and equipment	4,133	4,515
Network access
Depreciation and amortization allocation
Total depreciation and amortization of property and equipment	2,877	3,665
Network operations
Depreciation and amortization allocation
Total depreciation and amortization of property and equipment	808	674
Development and technology
Depreciation and amortization allocation
Total depreciation and amortization of property and equipment	416	150
General and administrative
Depreciation and amortization allocation
Total depreciation and amortization of property and equipment	32	26
Leasehold improvements
Property and equipment
Total property and equipment	77,115		72,119
Construction in progress
Property and equipment
Total property and equipment	11,507		6,295
Computer equipment
Property and equipment
Total property and equipment	7,457		7,493
Software
Property and equipment
Total property and equipment	7,886		7,519
Office equipment
Property and equipment
Total property and equipment	$ 411		$ 411