Investments

12 Months Ended

Dec. 31, 2015

Investments [Abstract]

Investments

Investments

The following tables summarize the Company's short-term and long-term investments (in thousands):

	December 31, 2015
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Certificates of deposit	$	30,724	$	2	$	(28	)	$	30,698
U.S. Treasury securities	292,264		—		(678		)	291,586
Preferred stock of U.S. corporation	1,545		—		(60		)	1,485
Total investments	$	324,533	$	2	$	(766	)	$	323,769

	December 31, 2014
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Certificates of deposit	$	28,039	$	1	$	(62	)	$	27,978
Corporate bonds	69,947		—		(56		)	69,891
Commercial paper	11,242		—		(2		)	11,240
U.S. Treasury securities	48,279		—		(82		)	48,197
Preferred stock of U.S. corporation	1,545		236		—			1,781
Total investments	$	159,052	$	237	$	(202	)	$	159,087

The following tables summarize the Company's investments with unrealized losses, aggregated by investment type and the length of time that individual investments have been in a continuous unrealized loss position (in thousands, except number of securities):

	December 31, 2015
	Less than 12 Months					Greater than 12 Months				Total
	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
Certificates of deposit	$	24,450	$	(28	)	$	—	$	—	$	24,450	$	(28	)
U.S. Treasury securities	291,586		(678		)	—		—		291,586		(678		)
Preferred stock of U.S. corporation	1,485		(60		)	—		—		1,485		(60		)
Total	$	317,521	$	(766	)	$	—	$	—	$	317,521	$	(766	)
Number of securities with unrealized losses			180					—				180

	December 31, 2014
	Less than 12 Months					Greater than 12 Months				Total
	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
Certificates of deposit	$	26,778	$	(62	)	$	—	$	—	$	26,778	$	(62	)
Corporate bonds	68,891		(56		)	—		—		68,891		(56		)
Commercial paper	8,740		(2		)	—		—		8,740		(2		)
U.S. Treasury securities	48,196		(82		)	—		—		48,196		(82		)
Total	$	152,605	$	(202	)	$	—	$	—	$	152,605	$	(202	)
Number of securities with unrealized losses			176					—				176

The following table summarizes the scheduled maturity for the Company's investments at December 31, 2015 (in thousands):

	December 31, 2015
Maturing in one year or less	$	198,244
Maturing after one year through two years	124,040
Total debt investments	$	322,284
Preferred stock of U.S. corporation	1,485
Total investments	$	323,769