Income Taxes - Reconciliation of Effective Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Effective Income Tax Rate Reconciliation Line Items [Abstract]
Income tax expense (benefit) at statutory federal rate	35.00%	(35.00%)	(35.00%)
State income tax expense (benefit), net of federal benefit	7.20%	(2.90%)	(2.70%)
Permanent differences and other	14.80%	1.40%	0.70%
Research and development credits, current year	(58.10%)	(2.60%)	(2.70%)
Research and development credits, prior year	(39.10%)	0.00%	0.00%
Change in effective state tax rates	(25.60%)	2.40%	10.30%
Expiration of net operating loss carryovers	8.20%	36.60%	9.40%
Stock compensation expense	53.70%	0.00%	(0.90%)
Reserve for uncertain tax positions and other reserves	5.40%	(2.40%)	3.10%
Change in valuation allowance	(22.20%)	1.00%	20.30%
Provision (benefit) for income taxes	(20.70%)	(1.50%)	2.50%