Marketable Investments (Tables)

9 Months Ended

Sep. 30, 2012

Marketable Investments

Schedule of marketable investments classified as held-to-maturity

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Government-sponsored enterprises at September 30, 2012	$	285,999	$	266	$	(32	)	$	286,233
Corporate notes and bonds at September 30, 2012	202,388		300		(20		)	202,668
Total	$	488,387	$	566	$	(52	)	$	488,901
Reported under the following captions on the consolidated balance sheet at September 30, 2012:
Current marketable investments	$	240,032
Noncurrent marketable investments	248,355
	$	488,387

	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Government-sponsored enterprises at December 31, 2011	$	308,202	$	155	$	(170	)	$	308,187
Corporate notes and bonds at December 31, 2011	276,118		113		(442		)	275,789
Total	$	584,320	$	268	$	(612	)	$	583,976
Reported under the following captions on the consolidated balance sheet at December 31, 2011:
Current marketable investments	$	240,803
Noncurrent marketable investments	343,517
	$	584,320

Summary of gross unrealized losses and the length of time marketable investments have been in a continuous unrealized loss position

	As of September 30, 2012					As of December 31, 2011
	Fair Value		Gross Unrealized Loss			Fair Value		Gross Unrealized Loss
Government-sponsored enterprises:
Continuous unrealized loss position less than one year	$	53,646	$	(32	)	$	170,018	$	(170	)
Continuous unrealized loss position greater than one year	—		—			—		—
	53,646		(32		)	170,018		(170		)
Corporate notes and bonds:
Continuous unrealized loss position less than one year	$	32,327	$	(20	)	$	149,383	$	(442	)
Continuous unrealized loss position greater than one year	—		—			—		—
	32,327		(20		)	149,383		(442		)
Total	$	85,973	$	(52	)	$	319,401	$	(612	)

Summary of the contractual maturities of held-to-maturity marketable investments

	September 30, 2012
	Amortized Cost		Fair Value
Due in less than one year	$	240,032	$	240,342
Due in one to two years	248,355		248,559
Due in three to five years	—		—
Due after five years	—		—
Total	$	488,387	$	488,901