Short-term Investments

6 Months Ended

Jun. 30, 2013

Investments Debt And Equity Securities [Abstract]

Short-term Investments

4. Short-term Investments

The Company’s short-term investments have remaining maturities of less than twelve months and are classified as available-for-sale. The following table summarizes the amortized cost, gross unrealized gains and losses and fair value of short-term investments as of June 30, 2013:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Aggregate Fair Value
U.S. government debt securities	$	87,453	$	—	$	(11	)	$	87,442
Commercial paper		5,999		—		—			5,999
Certificates of deposit		2,017		—		(4	)		2,013
Total	$	95,469	$	—	$	(15	)	$	95,454

For more information on our method for determining the fair value of our assets, see Note 2 – “Fair Value of Financial Instruments”.

Changes in market interest rates and bond yields cause certain of our short-term investments to fall below their cost basis, resulting in unrealized losses on short-term investments. As of June 30, 2013, we had unrealized losses of $15 related to short-term investments that had a fair value of $77,186. The unrealized losses of the Company’s short-term investments were primarily a result of unfavorable changes in interest rates subsequent to the initial purchase of these investments and have been in a loss position for less than 12 months.

As of June 30, 2013, we did not consider any of our short-term investments to be other-than-temporarily impaired. When evaluating our short-term investments for other-than-temporary impairment, we review factors such as the length of time and extent to which fair value has been below its cost basis, the financial condition of the issuer, our ability and intent to hold the security and whether it is more likely than not that we will be required to sell the investment before recovery of its cost basis.