Income Taxes - Reconciliation of Effective Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
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	4.80%	7.20%	(2.90%)
Permanent differences and other	(2.90%)	14.80%	1.40%
Research and development credits, current year	0.00%	(58.10%)	(2.60%)
Research and development credits, prior year	0.00%	(39.10%)	0.00%
Change in effective state tax rates	(3.20%)	(25.60%)	2.40%
Expiration of net operating loss carryovers	1.10%	8.20%	36.60%
Stock compensation expense	0.10%	53.70%	0.00%
Reserve for uncertain tax positions and other reserves	0.00%	5.40%	(2.40%)
Change in valuation allowance	(32.50%)	(22.20%)	1.00%
Provision (benefit) for income taxes	2.40%	(20.70%)	(1.50%)