MARKETABLE SECURITIES

12 Months Ended

Dec. 31, 2016

Investments Debt And Equity Securities [Abstract]

MARKETABLE SECURITIES

5. MARKETABLE SECURITIES

The following tables summarize the fair value, accumulated other comprehensive income (loss) and intraperiod tax allocation regarding our investment in Regulus available-for-sale marketable securities at December 31, 2016 and 2015, and for the activity recorded in each year, in thousands: 

Description	At December31, 2015			Salesof Regulus Shares During Year Ended December 31, 2016			All Other Activity During YearEnded December 31, 2016			Balance at December31, 2016
Carrying value	$	11,935		$	(3,842	)	$	—		$	8,093
Accumulated other comprehensive income (loss), before tax		39,484			(6,977	)		(31,603	)		904
Investment in equity securities of Regulus Therapeutics    Inc., as reported	$	51,419		$	(10,819	)	$	(31,603	)	$	8,997
Accumulated other comprehensive income (loss), before tax	$	39,484		$	(6,977	)	$	(31,603	)	$	904
Intraperiod tax allocation recorded as a benefit from    income taxes		(32,792	)		—			—			(32,792	)
Accumulated other comprehensive income (loss), net of tax	$	6,692		$	(6,977	)	$	(31,603	)	$	(31,888	)

Description	At December31, 2014			Salesof Regulus Shares During Year Ended December 31, 2015		All Other Activity During YearEnded December 31, 2015			Balance at December31, 2015
Carrying value	$	11,935		$	—	$	—		$	11,935
Accumulated other comprehensive income (loss), before tax		82,648			—		(43,164	)		39,484
Investment in equity securities of Regulus Therapeutics    Inc., as reported	$	94,583		$	—	$	(43,164	)	$	51,419
Accumulated other comprehensive income (loss), before tax	$	82,648		$	—	$	(43,164	)	$	39,484
Intraperiod tax allocation recorded as a benefit from    income taxes		(32,792	)		—		—			(32,792	)
Accumulated other comprehensive income (loss), net of tax	$	49,856		$	—	$	(43,164	)	$	6,692

We obtain fair value measurement data for our marketable securities from independent pricing services. We perform validation procedures to ensure the reasonableness of this data. This includes meeting with the independent pricing services to understand the methods and data sources used. Additionally, we perform our own review of prices received from the independent pricing services by comparing these prices to other sources and confirming those securities are trading in active markets.

The following tables summarize our marketable securities, other than our holdings in Regulus noted above, at December 31, 2016 and 2015, in thousands:

	At December 31, 2016
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Certificates of deposit	$	17,999	$	—	$	—		$	17,999
Commercial paper		59,340		—		—			59,340
Corporate notes		334,266		47		(441	)		333,872
U.S. government-sponsored enterprise securities		298,910		9		(1,146	)		297,773
U.S. treasury securities		40,022		1		(23	)		40,000
Total	$	750,537	$	57	$	(1,610	)	$	748,984

	At December 31, 2015
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Certificates of deposit	$	10,498	$	—	$	—		$	10,498
Commercial paper		38,113		—		(3	)		38,110
Corporate notes		907,119		4		(2,214	)		904,909
Municipal debt securities		9,000		—		—			9,000
U.S. government-sponsored enterprise securities		61,463		24		(91	)		61,396
U.S. treasury securities		76,186		4		(47	)		76,143
Total	$	1,102,379	$	32	$	(2,355	)	$	1,100,056

We classify our debt security investments based on their contractual maturity dates. The following table summarizes our available-for-sale debt securities by contractual maturity, at December 31, 2016, in thousands:

	At December 31, 2016
	Amortized Cost		Fair Value
Less than one year	$	424,382	$	424,185
Greater than one year but less than two years		326,155		324,799
Total	$	750,537	$	748,984