Marketable Securities (Tables)

3 Months Ended

Mar. 31, 2014

Investments, Debt and Equity Securities [Abstract]

Available-for-sale Securities

The following tables summarize the Company's investments in marketable securities at March 31, 2014 and December 31, 2013.

	Amortized		Unrealized					Fair
At March 31, 2014	Cost Basis		Gains		Losses			Value
U.S. government and government agency obligations	$	78,196	$	82	$	(13	)	$	78,265
Corporate bonds	579,600		517		(489		)	579,628
Municipal bonds	43,276		138		(13		)	43,401
International government agency obligations	8,214		3		—			8,217
Certificates of deposit	7,914		4		—			7,918
Equity securities	1,166		2,369		—			3,535
Total marketable securities	$	718,366	$	3,113	$	(515	)	$	720,964
At December 31, 2013
U.S. government and government agency obligations	$	107,493	$	55	$	(27	)	$	107,521
Corporate bonds	369,321		233		(361		)	369,193
Commercial paper	23,891		53		—			23,944
Municipal bonds	36,935		45		(59		)	36,921
International government agency obligations	2,007		1		—			2,008
Certificates of deposit	7,509		5		—			7,514
Equity securities	1,166		—		—			1,166
Total marketable securities	$	548,322	$	392	$	(447	)	$	548,267

Marketable Securities, Based on Contractual Maturity Dates

The fair values of debt security investments by contractual maturity as of March 31, 2014 and December 31, 2013 consist of the following:

	March 31, 2014		December 31, 2013
Maturities within one year	$	186,275	$	158,376
Maturities after one year through five years	525,961		383,410
Maturities after five years through ten years	4,042		4,138
Maturities after ten years	1,151		1,177
	$	717,429	$	547,101

Fair Value and Unrealized Losses of Marketable Securities

The following table shows the fair value of the Company’s marketable securities that have unrealized losses and that are deemed to be only temporarily impaired, aggregated by investment category and length of time that the individual securities have been in a continuous unrealized loss position, at March 31, 2014 and December 31, 2013.

	Less than 12 Months					12 Months or Greater		Total
At March 31, 2014	Fair Value		Unrealized Loss			Fair Value	Unrealized Loss	Fair Value		Unrealized Loss
U.S. government and government agency obligations	$	5,983	$	(13	)	—	—	$	5,983	$	(13	)
Corporate bonds	268,174		(489		)	—	—	268,174		(489		)
Municipal bonds	12,187		(13		)	—	—	12,187		(13		)
	$	286,344	$	(515	)	—	—	$	286,344	$	(515	)
At December 31, 2013
U.S. government and government agency obligations	$	49,241	$	(27	)	—	—	$	49,241	$	(27	)
Corporate bonds	176,140		(361		)	—	—	176,140		(361		)
Municipal bonds	14,431		(59		)	—	—	14,431		(59		)
	$	239,812	$	(447	)	—	—	$	239,812	$	(447	)