Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2013

Investments, Debt and Equity Securities [Abstract]

Available-for-sale Securities

The following tables summarize the Company's investments in marketable securities at December 31, 2013 and 2012.

	Amortized		Unrealized					Fair
At December 31, 2013	Cost Basis		Gains		Losses			Value
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

At December 31, 2012
Unrestricted
U.S. government and government agency obligations	$	327,502	$	661	$	(17	)	$	328,146
Municipal bonds	17,542		—		(32		)	17,510
Equity securities	4,044		—		(651		)	3,393
	349,088		661		(700		)	349,049
Restricted
U.S. government obligations	5,902		9		(2		)	5,909
	$	354,990	$	670	$	(702	)	$	354,958

Marketable Securities, Based on Contractual Maturity Dates

The fair values of debt security investments by contractual maturity as of December 31, 2013 and 2012 consist of the following:

	2013		2012
Unrestricted
Maturities within one year	$	158,376	$	77,819
Maturities after one year through five years	383,410		267,837
Maturities after five years through ten years	4,138		—
Maturities after ten years	1,177		—
	547,101		345,656
Restricted
Maturities within one year	—		2,781
Maturities after one year through five years	—		3,128
	—		5,909
	$	547,101	$	351,565

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 December 31, 2013 and 2012.

	Less than 12 Months					12 Months or Greater					Total
At December 31, 2013	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
Unrestricted
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	)
At December 31, 2012
Unrestricted
U.S. government and government agency obligations	$	44,738	$	(17	)	—		—			$	44,738	$	(17	)
Municipal bonds	17,510		(32		)	—		—			17,510		(32		)
Equity securities	—		—			$	3,393	$	(651	)	3,393		(651		)
	62,248		(49		)	3,393		(651		)	65,641		(700		)
Restricted
U.S government obligations	1,194		(2		)	—		—			1,194		(2		)
	$	63,442	$	(51	)	$	3,393	$	(651	)	$	66,835	$	(702	)