Income Taxes - Components of Deferred Tax Assets and Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Deferred tax assets:
Net operating losses	$ 1,420	$ 1,300
Tax credits	2,039	911
Deferred revenue	4,186	7,021
Stock compensation	2,174	3,718
Accrued expenses	849	1,388
Deferred Tax Assets, Charitable Contribution Carryforwards	20	0
Total deferred tax assets	10,688	14,338
Total deferred tax assets	(904)	(668)
Deferred tax assets, net of valuation allowance	9,784	13,670
Fixed assets	(1,902)	(2,126)
Intangible assets	(1,709)	(2,875)
Net deferred tax assets	$ 6,173	$ 8,669