SHORT-TERM INVESTMENTS

3 Months Ended

Mar. 31, 2016

SHORT-TERM INVESTMENTS

SHORT-TERM INVESTMENTS

3. SHORT-TERM INVESTMENTS(in thousands)

        As of March 31, 2016, short-term investments consisted of the following:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Available-for-sale securities:
Corporate notes and bonds	$	407,461	$	620	$	(528	)	$	407,553
U.S. agency obligations		97,562		43		(13	)		97,592
U.S. treasury securities		70,291		76		(27	)		70,340
Commercial paper		29,798		66		(6	)		29,858
Certificates of deposit		6,251		4		—			6,255
Total available-for-sale securities	$	611,363	$	809	$	(574	)	$	611,598

        As of December 31, 2015, short-term investments consisted of the following:

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Available-for-sale securities:
Corporate notes and bonds	$	390,185	$	12	$	(2,321	)	$	387,876
U.S. agency obligations		121,521		11		(203	)		121,329
U.S. treasury securities		60,362		2		(179	)		60,185
Commercial paper		36,849		—		(28	)		36,821
Certificates of deposit		7,928		—		(9	)		7,919
Total available-for-sale securities	$	616,845	$	25	$	(2,740	)	$	614,130

        The following table summarizes the estimated fair value of our short-term investments, designated as available-for-sale and classified by the contractual maturity date of the securities as of the dates shown:

	March 31, 2016		December 31, 2015
Due in one year or less	$	217,876	$	206,679
Due after one year through three years		393,722		407,451
Total	$	611,598	$	614,130

        The Company has certain available-for-sale securities in a gross unrealized loss position, all of which have been in such position for less than 12 months. The Company reviews its debt securities classified as short-term investments on a regular basis to evaluate whether or not any security has experienced an other-than-temporary decline in fair value. The Company considers factors such as the length of time and extent to which the market value has been less than the cost, the financial position and near-term prospects of the issuer and the Company's intent to sell, or whether it is more likely than not the Company will be required to sell the investment before recovery of the investment's amortized-cost basis. If the Company determines that an other-than-temporary decline exists, or if write downs related to credit losses are necessary, in one of these securities, the unrealized losses attributable to the respective investment would be reclassified to realized losses on short-term investments within the statement of operations. There were no impairments considered other-than-temporary as of March 31, 2016.

        The following table shows the fair values and the gross unrealized losses of available-for-sale securities that have been in a gross unrealized loss position for less than 12 months, aggregated by investment category as of March 31, 2016:

	Estimated Fair Value		Gross Unrealized Losses
Corporate notes and bonds	$	257,125	$	(528	)
U.S. agency obligations		30,585		(13	)
U.S. treasury securities		50,977		(27	)
Commercial paper		12,475		(6	)
Certificates of deposit		961		—
	$	352,123	$	(574	)