Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2013

Accounting Policies [Abstract]

Marketable Securities

At March 31, 2013, marketable securities by security type consisted of:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
U.S. Treasury Notes	$	10,110	$	20	$	—		$	10,130
Corporate and Agency Bonds		910		—		(2	)		908
Certificates of Deposit		1,000		—		—			1,000
Commercial Paper		2,896		—		—			2,896
Total	$	14,916	$	20	$	(2	)	$	14,934

At March 31, 2013, marketable securities consisted of investments that mature within one year.

At December 31, 2012, marketable securities by security type consisted of:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
U.S. Treasury Notes	$	10,138		20	$	—	$	10,158
Corporate and Agency Bonds		12,675		1		—		12,676
Certificates of Deposit		1,000		—		—		1,000
Commercial Paper		1,898		—		—		1,898
Total	$	25,711	$	21	$	—	$	25,732

Fair Value Hierarchy for Cash Equivalents and Marketable Securities Measured at Fair Value on Recurring Basis

The following tables present the Company’s fair value hierarchy for its cash equivalents and marketable securities which are measured at fair value on a recurring basis as of March 31, 2013 and December 31, 2012:

	Fair Value Measurements at March 31, 2013 Using
	Level 1		Level 2		Level 3		Total
Financial Assets:
Money Market Instruments	$	49,288	$	—	$	—	$	49,288
U.S. Treasury Notes		10,130		—		—		10,130
Corporate and Agency Bonds		—		908		—		908
Certificates of Deposit		—		1,000		—		1,000
Commercial Paper		—		2,896		—		2,896
Total	$	59,418	$	4,804	$	—	$	64,222

	Fair Value Measurements at December 31, 2012 Using
	Level 1		Level 2		Level 3		Total
Financial Assets:
Money Market Instruments	$	38,320	$	—	$	—	$	38,320
U.S. Treasury Notes		10,158		—		—		10,158
Corporate and Agency Bonds		—		12,676		—		12,676
Certificates of Deposit		—		1,000		—		1,000
Commercial Paper		—		1,898		—		1,898
Total	$	48,478	$	15,574	$	—	$	64,052

Estimated Useful Lives of Assets

Estimated useful lives of assets are as follows:

Computer equipment	3 years
Software	3 years
Furniture and fixtures	5 years
Leasehold improvements	Shorter of life of lease or estimated useful life

Shares Used in Computing Diluted Net Income (Loss) Per Share

The following is a summary of the shares used in computing diluted net income (loss) per share:

(in thousands)

	Three months ended March 31,
	2013		2012
Weighted average shares used in calculating basic net income (loss) per share		30,630		30,171
Stock options		—		905
Warrants		—		1
Unvested restricted shares and restricted share units		—		41
Shares used in computing diluted net income (loss) per share		30,630		31,118

Common Stock Equivalents Excluded from Computation of Diluted Net Income (Loss) Per Share

The following common stock equivalents were excluded from the computation of diluted net income (loss) per share because they had an anti-dilutive impact either because the proceeds under the treasury stock method were in excess of the average fair market value for the period or because the Company had a net loss in the period:

(in thousands)

	Three months ended March 31,
	2013		2012
Options to purchase common stock		5,538		2,051
Unvested restricted stock and restricted stock units		588		15
Warrants to purchase common stock		1		—
Total options and warrants exercisable into common stock, restricted stock units issuable in common stock and restricted stock		6,127		2,066