Income Taxes (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Reconciliation of the Company's effective tax rate to the statutory federal income tax rate
Federal statutory rate (as a percent)	35.00%	35.00%	35.00%
State taxes, net of Federal benefit (as a percent)	4.50%	4.20%	4.60%
Permanent differences (as a percent)	(0.20%)	(0.40%)	(2.60%)
Stock compensation (as a percent)	(0.30%)	(1.20%)	(2.90%)
Change in valuation allowance (as a percent)	(35.50%)	(36.30%)	(39.20%)
Tax credits (as a percent)	1.10%	3.90%	5.10%
Foreign rate differentials (as a percent)	(4.10%)	(4.40%)
Other (as a percent)	(0.50%)	(0.80%)
Deferred tax assets
Net operating losses	$ 77,806	$ 40,633
Capitalized research and development expenses	40,083	47,640
Credit carryforwards	14,398	13,380
Depreciation	2,931	2,337
Deferred compensation	5,068	4,450
Deferred revenue	29,936	26,462
Accrued expenses	1,184	676
Others	1,934	922
Total gross deferred tax asset	173,340	136,500
Intangible assets	(3,689)	(3,817)
Valuation allowance	$ (169,651)	$ (132,683)