SHORT-TERM INVESTMENTS

3 Months Ended

Mar. 31, 2017

SHORT-TERM INVESTMENTS

SHORT-TERM INVESTMENTS

3.SHORT-TERM INVESTMENTS (in thousands)

        As of March 31, 2017, 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	$	318,459	$	62	$	(637	)	$	317,884
U.S. agency obligations		34,855		15		(72	)		34,798
U.S. treasury securities		31,147		3		(93	)		31,057
Commercial paper		—		—		—			—
Certificates of deposit		1,683		—		—			1,683
Total available-for-sale securities	$	386,144	$	80	$	(802	)	$	385,422

        As of December 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	$	349,571	$	36	$	(918	)	$	348,689
U.S. agency obligations		34,864		22		(78	)		34,808
U.S. treasury securities		53,681		6		(100	)		53,587
Commercial paper		6,312		—		(3	)		6,309
Certificates of deposit		1,921		1		—			1,922
Total available-for-sale securities	$	446,349	$	65	$	(1,099	)	$	445,315

        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, 2017		December 31, 2016
Due in one year or less	$	186,057	$	176,696
Due after one year through three years		199,365		268,619
Total	$	385,422	$	445,315

        The Company has certain available-for-sale securities in a gross unrealized loss position. 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, 2017.

        The following table shows the fair values and the gross unrealized losses of available-for-sale securities that were in a gross unrealized loss position, as of March 31, 2017, aggregated by investment category:

	Estimated Fair Value		Gross Unrealized Losses
Corporate notes and bonds	$	255,307	$	(637	)
U.S. agency obligations		22,978		(72	)
U.S. treasury securities		26,836		(93	)
	$	305,121	$	(802	)