SHORT-TERM INVESTMENTS

6 Months Ended

Jun. 30, 2017

Investments, Debt and Equity Securities [Abstract]

SHORT-TERM INVESTMENTS

SHORT-TERM INVESTMENTS(in thousands)

As of June 30, 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	$	291,494	$	65	$	(454	)	$	291,105
U.S. agency obligations	27,857		3		(53		)	27,807
U.S. treasury securities	20,736		—		(112		)	20,624
Total available-for-sale securities	$	340,087	$	68	$	(619	)	$	339,536

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:

	June 30, 2017		December 31, 2016
Due in one year or less	$	192,204	$	176,696
Due after one year through three years	147,332		268,619
Total	$	339,536	$	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 June 30, 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 June 30, 2017, aggregated by investment category:

	Estimated Fair Value		Gross Unrealized Losses
Corporate notes and bonds	$	225,931	$	(454	)
U.S. agency obligations	17,795		(53		)
U.S. treasury securities	20,624		(112		)
	$	264,350	$	(619	)