Fair Value Hierarchy (Tables)

9 Months Ended

Sep. 30, 2012

Fair Value Hierarchy [Abstract]

Presentation of financial assets and liabilities measured at fair value on a recurring basis

	Total		Level 1		Level 2		Level 3
	(in thousands)
Assets
Money market funds(1)	$	57,918	$	57,918	$	—	$	—
U.S. government bonds and notes(2)		22,052		22,052		—		—
Total available-for-sale debt securities	$	79,970	$	79,970	$	—	$	—

(1) Money market funds are included in cash and cash equivalents on the condensed consolidated balance sheet.

(2) U.S. government bonds and notes are included in marketable securities on the condensed consolidated balance sheet

	Total			Level 1		Level 2		Level 3
	(in thousands)
Assets
Money market funds(1)	$	2,062		$	2,062	$	—	$	—
Liabilities
Convertible preferred stock warrants(2)	$	(1,137	)	$	—	$	—	$	(1,137	)

(1) Money market funds are included in cash and cash equivalents on the condensed consolidated balance sheet.

(2) The convertible preferred stock warrants were subject to revaluation at each balance sheet date and any change in fair value was recognized as a component of other income (expense), net in the consolidated statements of comprehensive income. These warrants were revalued up to the date the convertible preferred stock warrants were exercised or became warrants to purchase common stock upon the closing of our IPO, and the liability related to these warrants were reclassified as stockholders’ equity (deficit).

Reconciliations of convertible preferred stock warrants

	September 30, 2012			December 31, 2011
	(in thousands)
Beginning balance	$	1,137		$	315
Change in fair value of preferred stock warrants		290			822
Exercise of preferred stock warrants		(1,404	)		—
Conversion of preferred stock warrants to common stock warrants		(23	)		—
Ending balance	$	—		$	1,137