Investments (Tables)

9 Months Ended

Sep. 30, 2015

Investments [Abstract]

Contract Maturity of Available-for-Sale Securities

The following table summarizes the contract maturity of the available-for-sale securities we held as of September 30, 2015:

One year or less	52%
After one year but within two years	28%
After two years but within three and a half years	20%
Total	100%

Summary of Investments

The following is a summary of our investments (in thousands):

			Gross Unrealized					Other- Than- Temporary Impairment			Estimated
September 30, 2015	Cost		Gains		Losses			Loss			Fair Value
Available-for-sale securities (1):
Corporate debt securities	$	178,172	$	37	$	(88	)	$	—		$	178,121
Debt securities issued by U.S. government agencies		91,609		8		(6	)		—			91,611
Debt securities issued by states of the United States and political subdivisions of the states (2)		62,048		36		(59	)		—			62,025
Total securities with a maturity of one year or less		331,829		81		(153	)		—			331,757
Corporate debt securities		270,045		132		(701	)		—			269,476
Debt securities issued by U.S. government agencies		30,654		19		(2	)		—			30,671
Debt securities issued by states of the United States and political subdivisions of the states		61,388		28		(121	)		—			61,295
Total securities with a maturity of more than one year		362,087		179		(824	)		—			361,442
Total available-for-sale securities	$	693,916	$	260	$	(977	)	$	—		$	693,199
Equity securities:
Regulus Therapeutics Inc.	$	7,162	$	11,432	$	—		$	—		$	18,594
Securities included in other current assets		880		—		—			(880	)		—
Total equity securities	$	8,042	$	11,432	$	—		$	(880	)	$	18,594
Total available-for-sale and equity securities	$	701,958	$	11,692	$	(977	)	$	(880	)	$	711,793

			Gross Unrealized					Other- Than- Temporary Impairment			Estimated
December 31, 2014	Cost		Gains		Losses			Loss			Fair Value
Available-for-sale securities (1):
Corporate debt securities (2)	$	219,856	$	89	$	(89	)	$	—		$	219,856
Debt securities issued by U.S. government agencies		47,496		7		(27	)		—			47,476
Debt securities issued by the U.S. Treasury (2)		19,008		9		—			—			19,017
Debt securities issued by states of the United States and political subdivisions of the states (2)		45,196		19		(53	)		—			45,162
Total securities with a maturity of one year or less		331,556		124		(169	)		—			331,511
Corporate debt securities		152,730		16		(600	)		—			152,146
Debt securities issued by U.S. government agencies		62,530		—		(151	)		—			62,379
Debt securities issued by states of the United States and political subdivisions of the states		60,073		32		(234	)		—			59,871
Total securities with a maturity of more than one year		275,333		48		(985	)		—			274,396
Total available-for-sale securities	$	606,889	$	172	$	(1,154	)	$	—		$	605,907
Equity securities:
Regulus Therapeutics Inc.	$	12,477	$	69,404	$	—		$	—		$	81,881
Securities included in other current assets		880		—		—			(880	)		—
Total equity securities	$	13,357	$	69,404	$	—		$	(880	)	$	81,881
Total available-for-sale and equity securities	$	620,246	$	69,576	$	(1,154	)	$	(880	)	$	687,788

(1) Our available-for-sale securities are held at amortized cost.

(2) Includes investments classified as cash equivalents on our condensed consolidated balance sheet.

Temporarily Impaired Investments

Investments we considered to be temporarily impaired at September 30, 2015 were as follows (in thousands):

			Less than 12 months of temporary impairment					More than 12 months of temporary impairment					Total temporary impairment
	Number of Investments		Estimated Fair Value		Unrealized Losses			Estimated Fair Value		Unrealized Losses			Estimated Fair Value		Unrealized Losses
Corporate debt securities		247	$	293,774	$	(773	)	$	9,421	$	(16	)	$	303,195	$	(789	)
Debt securities issued by U.S. government agencies		7		40,497		(8	)		—		—			40,497		(8	)
Debt securities issued by states of the United States and political subdivisions of the states		96		50,648		(72	)		14,899		(108	)		65,547		(180	)
Total temporarily impaired securities		350	$	384,919	$	(853	)	$	24,320	$	(124	)	$	409,239	$	(977	)