Income Taxes (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating loss carryforwards
Net increase in valuation allowance	$ 74,000,000	$ 47,900,000	$ 22,600,000
Deferred tax liabilities	0
Unrecognized deferred tax benefits	18,100,000
Unrecognized deferred tax benefits related to stock option exercises, accounted for as a credit to additional paid-in capital realized through a reduction in income taxes payable	81,000
Federal income tax
Operating loss carryforwards
Net operating loss carryforwards to reduce future taxable income	545,100,000
State income tax
Operating loss carryforwards
Net operating loss carryforwards to reduce future taxable income	$ 229,100,000