Marketable Securities

3 Months Ended

Mar. 31, 2013

Investments, Debt and Equity Securities [Abstract]

Marketable Securities

Marketable Securities

Marketable securities at March 31, 2013 and December 31, 2012 consist of debt and equity securities. The Company also held restricted marketable securities at both March 31, 2013 and December 31, 2012, which consisted of debt securities, as detailed below, that collateralize letters of credit and lease obligations.

The following tables summarize the amortized cost basis of debt and equity securities included in marketable securities, the aggregate fair value of those securities, and gross unrealized gains and losses on those securities at March 31, 2013 and December 31, 2012.

	Amortized		Unrealized					Fair
At March 31, 2013	Cost Basis		Gains		Losses			Value
Unrestricted
U.S. government and government agency obligations	$	305,402	$	568	$	(3	)	$	305,967
Corporate bonds	123,015		3		(148		)	122,870
Commercial paper	25,172							25,172
Municipal bonds	17,159		6		(4		)	17,161
Equity securities	4,044				(1,259		)	2,785
	474,792		577		(1,414		)	473,955
Restricted
U.S. government obligations	8,350		9		(1		)	8,358
	$	483,142	$	586	$	(1,415	)	$	482,313

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

The Company classifies its debt securities based on their contractual maturity dates. The debt securities listed at March 31, 2013 mature at various dates through January 2016. The fair values of debt security investments by contractual maturity as of March 31, 2013 and December 31, 2012 consist of the following:

	March 31,		December 31,
	2013		2012
Unrestricted
Maturities within one year	$	127,349	$	77,819
Maturities after one year through five years	343,821		267,837
	471,170		345,656
Restricted
Maturities within one year	6,868		2,781
Maturities after one year through five years	1,490		3,128
	8,358		5,909
	$	479,528	$	351,565

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, 2013 and December 31, 2012.

	Less than 12 Months					12 Months or Greater					Total
At March 31, 2013	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
Unrestricted
U.S. government and government agency obligations	$	25,004	$	(3	)						$	25,004	$	(3	)
Corporate bonds	114,555		(148		)						114,555		(148		)
Municipal bonds	6,490		(4		)						6,490		(4		)
Equity security						$	2,786	$	(1,259	)	2,786		(1,259		)
	146,049		(155		)	2,786		(1,259		)	148,835		(1,414		)
Restricted
U.S. government obligations	904		(1		)						904		(1		)
	$	146,953	$	(156	)	$	2,786	$	(1,259	)	$	149,739	$	(1,415	)
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 security						$	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	)

Realized gains and losses are included as a component of investment income. For the three months ended March 31, 2013 and 2012, total realized gains and losses on sales of marketable securities were not material.