Investments

The following tables summarize the Company’s investments (in thousands):



	January 28, 2017
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Short-term investments:
Available-for-sale:
Corporate debt securities	$	432,603	$	281	$	(776	)	$	432,108
U.S. government and agency debt	185,584		86		(283		)	185,387
Asset backed securities	45,541		33		(47		)	45,527
Foreign government and agency debt	13,425		—		(50		)	13,375
Municipal debt securities	27,916		4		(49		)	27,871
Held-to-Maturity:
Time deposits	150,000		—		—			150,000
Total short-term investments	855,069		404		(1,205		)	854,268
Long-term investments:
Available-for-sale:
Auction rate securities	4,615		—		—			4,615
Total long-term investments	4,615		—		—			4,615
Total investments	$	859,684	$	404	$	(1,205	)	$	858,883



	January 30, 2016
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Short-term investments:
Available-for-sale:
Corporate debt securities	$	558,337	$	766	$	(1,282	)	$	557,821
U.S. government and agency debt	317,595		64		(254		)	317,405
Asset backed securities	76,711		81		(56		)	76,736
Foreign government and agency debt	21,370		2		(14		)	21,358
Municipal debt securities	31,211		45		(7		)	31,249
Total short-term investments	1,005,224		958		(1,613		)	1,004,569
Long-term investments:
Available-for-sale:
Auction rate securities	11,296		—		—			11,296
Total long-term investments	11,296		—		—			11,296
Total investments	$	1,016,520	$	958	$	(1,613	)	$	1,015,865

As of January 28, 2017, the Company’s investment portfolio included auction rate securities with an aggregate par value of $5 million. Although these auction rate securities have continued to pay interest and the underlying collateral has not deteriorated, there is currently limited trading volume. The Company uses a discounted cash flow model to estimate the fair value of the auction rate securities based on its estimated timing and amount of future interest and principal payments. The fair value of the auction rate securities as of January 28, 2017 was $0.4 million less than the par value and is included in long-term investments.

The Company made a determination in January 2016 that it did not expect to recover the par value of these auction rate securities and considers any impairment of these securities to be other-than-temporary. There has been no change in circumstances since January 2016 based upon the current time horizon for holding these auction rate securities and the continuation of an illiquid market. Based on the Company's assessment of fair value as of January 28, 2017, the Company determined there was no further impairment of these auction rate securities.

During fiscal 2017, the Company sold auction rate securities with an aggregate par value of $7.5 million for total net proceeds of $6.9 million. The carrying value of these auction rate securities was $6.7 million and resulted in a net gain of $0.2 million recorded in interest and other income, net, in the year ended January 28, 2017.

Gross realized gains and gross realized losses on sales of available-for-sale securities are presented in the following table (in thousands):



	Year Ended
	January 28, 2017			January 30, 2016			January 31, 2015
Gross realized gains	$	2,047		$	1,654		$	1,618
Gross realized losses	(547		)	(1,923		)	(169		)
Impairment loss	—			(1,204		)	—
Total net realized gains (losses)	$	1,500		$	(1,473	)	$	1,449

The contractual maturities of available-for-sale securities are presented in the following table (in thousands):



	January 28, 2017				January 30, 2016
	Amortized Cost		Estimated Fair Value		Amortized Cost		Estimated Fair Value
Due in one year or less	$	423,151	$	423,058	$	304,117	$	304,035
Due between one and five years	423,669		422,995		689,847		689,279
Due over five years	12,864		12,830		22,556		22,551
	$	859,684	$	858,883	$	1,016,520	$	1,015,865

For individual securities that have been in a continuous unrealized loss position, the fair value and gross unrealized loss for these securities aggregated by investment category and length of time in an unrealized position are presented in the following tables (in thousands):



	January 28, 2017
	Less than 12 months					12 months or more					Total
	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
Corporate debt securities	$	199,382	$	(751	)	$	16,063	$	(25	)	$	215,445	$	(776	)
U.S. government and agency debt	94,064		(283		)	—		—			94,064		(283		)
Asset backed securities	16,754		(47		)	—		—			16,754		(47		)
Foreign government and agency debt	11,875		(48		)	1,499		(2		)	13,374		(50		)
Municipal debt securities	17,450		(47		)	1,248		(2		)	18,698		(49		)
Total securities	$	339,525	$	(1,176	)	$	18,810	$	(29	)	$	358,335	$	(1,205	)



	January 30, 2016
	Less than 12 months					12 months or more					Total
	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
Corporate debt securities	$	283,138	$	(1,237	)	$	14,383	$	(45	)	$	297,521	$	(1,282	)
U.S. government and agency debt	263,325		(254		)	—		—			263,325		(254		)
Asset backed securities	46,646		(56		)	—		—			46,646		(56		)
Foreign government and agency debt	16,458		(14		)	—		—			16,458		(14		)
Municipal debt securities	2,943		(5		)	1,571		(2		)	4,514		(7		)
Total securities	$	612,510	$	(1,566	)	$	15,954	$	(47	)	$	628,464	$	(1,613	)