CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Current assets:
Accounts receivable, allowance for doubtful accounts	$ 0	$ 2
Stockholders' equity:
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	150,000,000	150,000,000
Common stock, shares issued (in shares)	54,474,594	50,002,587
Common stock, shares outstanding (in shares)	53,281,996	49,809,989