Other Balance Sheet Items - Allowance for Doubtful Accounts and Reserve for Subscriber Refunds (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Allowance for doubtful accounts
Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	$ 400	$ 386	$ 501
Additions — charged to costs and expenses, or contra revenue, net	304	173	139
Additions — recoveries of amounts previously charged-off	0	(123)	60
Deductions — write-offs	(206)	(36)	(314)
Ending Balance	498	400	386
Reserve for subscriber refunds
Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	893	70	0
Additions — charged to costs and expenses, or contra revenue, net	1,269	1,931	70
Additions — recoveries of amounts previously charged-off	0	0	0
Deductions — write-offs	(1,172)	(1,108)	0
Ending Balance	$ 990	$ 893	$ 70