Property and Equipment - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Property, Plant and Equipment [Line Items]
Depreciation and amortization expense	$ 12,994	$ 9,547	$ 7,581
Depreciation and amortization expense, recorded in cost of subscription revenue	11,684	8,744	7,111
Carrying value of installed in-vehicle devices, net of accumulated depreciation	48,373	34,097
Capitalized costs, associated with development of internal-use software	2,225	883
Amortization expense of the internal-use software	482	573	336
Carrying value of capitalized internal-use software	3,192	1,328
Gross amount of assets under capital leases	1,593	1,121
Assets under capital leases, accumulated amortization	874	456
Expense associated with the replacement of installed in-vehicle devices that had become defective	$ 3,086	$ 2,150	$ 950