SHORT-TERM INVESTMENTS (Tables)

3 Months Ended

Mar. 31, 2016

SHORT-TERM INVESTMENTS

Schedule of short-term investments

        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

Summary of estimated fair value of short-term investments, designated as available-for-sale and classified by the contractual maturity

	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

Schedule of fair values and gross unrealized losses of available-for-sale securities aggregated by investment category

        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	)