Fair Value of Financial Instruments

9 Months Ended

Sep. 30, 2013

Fair Value Disclosures [Abstract]

Fair Value of Financial Instruments

3. Fair Value of Financial Instruments

Cash and Cash Equivalents

The Company considers all highly liquid investments with a remaining maturity at the date of purchase of 90 days or less to be cash equivalents. At September 30, 2013 and December 31, 2012, substantially all cash equivalents were U.S. treasury bills and amounts held in money market accounts at commercial banks.

Investments

All of the Company’s investments were classified as available-for-sale at September 30, 2013 and December 31, 2012. The principal amounts of short-term investments are summarized in the tables below:

	Less Than 12 Months to Maturity
	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
Balance at September 30, 2013:
U.S. Treasury securities	$	218,555	$	52	$	—	$	218,607
Total	$	218,555	$	52	$	—	$	218,607
Balance at December 31, 2012:
U.S. Treasury securities	$	195,055	$	15	$	—	$	195,070
Total	$	195,055	$	15	$	—	$	195,070

The Company completed an evaluation of its investments and determined that it did not have any other-than-temporary impairments as of September 30, 2013 or December 31, 2012.

Fair Value Measurements

Under current accounting standards, fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs.

The current accounting guidance also establishes a hierarchy to categorize how fair value is measured and which is based on three levels of inputs, of which the first two are considered observable and the last unobservable, as follows:

Level 1	Quoted prices in active markets for identical assets or liabilities.
Level 2	Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.
Level 3	Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.

The following table presents information about the Company’s financial assets and liabilities measured at fair value on a recurring basis as of September 30, 2013:

	September 30,  2013		Quoted Price in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets
Cash equivalents
Money market fund	$	32,275	$	32,275	$	—	$	—
Marketable securities
US treasury securities	$	218,607	$	218,607	$	—	$	—
Total	$	250,882	$	250,882	$	—	$	—

The following table presents information about the Company’s financial assets and liabilities measured at fair value on a recurring basis as of December 31, 2012:

	December 31, 2012		Quoted Price in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Assets
Cash equivalents
Money market fund	$	10,387	$	10,387	$	—	$	—
US treasury securities		10,011		10,011		—	$	—
Marketable securities
US treasury securities	$	195,070	$	195,070	$	—	$	—
Total	$	215,468	$	215,468	$	—	$	—