Marketable Securities (Tables)

9 Months Ended

Sep. 30, 2014

Investments, Debt and Equity Securities [Abstract]

The following tables summarize the Company's investments in marketable securities at September 30, 2014 and December 31, 2013.



	Amortized		Unrealized					Fair
At September 30, 2014	Cost Basis		Gains		Losses			Value
Unrestricted
U.S. government and government agency obligations	$	51,059	$	71	$	(1	)	$	51,129
Corporate bonds	696,149		574		(1,131		)	695,592
Municipal bonds	42,756		94		(8		)	42,842
Equity securities	1,166		3,933		—			5,099
	791,130		4,672		(1,140		)	794,662
Restricted
Equity securities	15,000		39,431		—			54,431
	$	806,130	$	44,103	$	(1,140	)	$	849,093

At December 31, 2013
Unrestricted
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
	$	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 September 30, 2014 and December 31, 2013 consist of the following:



	September 30, 2014		December 31, 2013
Maturities within one year	$	287,739	$	158,376
Maturities after one year through five years	496,700		383,410
Maturities after five years through ten years	5,124		4,138
Maturities after ten years	—		1,177
	$	789,563	$	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 September 30, 2014 and December 31, 2013.



	Less than 12 Months					12 Months or Greater		Total
At September 30, 2014	Fair Value		Unrealized Loss			Fair Value	Unrealized Loss	Fair Value		Unrealized Loss
U.S. government and government agency obligations	$	1,401	$	(1	)	—	—	$	1,401	$	(1	)
Corporate bonds	343,835		(1,131		)	—	—	343,835		(1,131		)
Municipal bonds	10,502		(8		)	—	—	10,502		(8		)
	$	355,738	$	(1,140	)	—	—	$	355,738	$	(1,140	)

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	)