Marketable Securities (Tables)

9 Months Ended

Sep. 30, 2013

Investments Debt And Equity Securities [Abstract]

Investments in Marketable Securities as Available for Sale

Our investments in marketable securities are classified as available for sale and are summarized as follows:

	September 30, 2013
	Amortized Cost		Unrealized Gain (Loss)			Market Value
	(In thousands)
U.S. Treasury Bills and Notes (due within one year)	$	799,981	$	(1	)	$	799,980
Mortgage-backed securities		212		12			224
Total	$	800,193	$	11		$	800,204
	December 31, 2012
	Amortized Cost		Unrealized Gain (Loss)			Market Value
	(In thousands)
U.S. Treasury Bills and Notes (due within one year)	$	1,149,707	$	150		$	1,149,857
Mortgage-backed securities		276		25			301
Total	$	1,149,983	$	175		$	1,150,158

Summary of Proceeds from Sales and Maturities of Marketable Securities and Gross Realized Gains and Losses

Proceeds from maturities and sales of marketable securities and gross realized gains and losses are summarized as follows:

	Three Months Ended						Nine Months Ended
	September 30,						September 30,
	2013			2012			2013			2012
	(In thousands)
Proceeds from maturities	$	1,475,000		$	675,000		$	3,225,000		$	1,925,000
Proceeds from sales		25			56			62			150,106
Gross realized gains		—			—			—			—
Gross realized losses		(1	)		(1	)		(1	)		(6	)