Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2011

Fair Value Measurements [Abstract]

Assets measured at fair value on a recurring basis

The Company’s assets measured at fair value on a recurring basis at December 31, 2011 were as follows:

							Fair Value Measurements at Reporting Date Using
	Fair Value of Cash Equivalents		Fair Value of Available-for- Sale Securities		Total Fair Value		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Auction rate securities	$	—	$	11,551	$	11,551	$	—	$	—	$	11,551
Certificates of deposit		105,017		118,094		223,111		—		223,111		—
Commercial paper		26,617		172,564		199,181		—		199,181		—
Corporate bonds		—		566,724		566,724		—		566,724		—
Debt securities of government sponsored entities		—		290,543		290,543		290,543		—		—
Equity index funds		—		40,843		40,843		40,843		—		—
Money market funds		404,757		15,067		419,824		419,824		—		—
Municipal bonds		3,121		399,026		402,147		—		402,147		—
U.S. Treasury securities		—		26,124		26,124		26,124		—		—
Total assets measured at fair value	$	539,512	$	1,640,536	$	2,180,048	$	777,334	$	1,391,163	$	11,551

The Company’s assets measured at fair value on a recurring basis at December 31, 2010 were as follows:

							Fair Value Measurements at Reporting Date Using
	Fair Value of Cash Equivalents		Fair Value of Available-for- Sale Securities		Total Fair Value		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Auction rate securities	$	—	$	21,293	$	21,293	$	—	$	—	$	21,293
Certificates of deposit		137,215		13,651		150,866		—		150,866		—
Commercial paper		34,742		14,793		49,535		—		49,535		—
Corporate bonds		1,002		237,916		238,918		—		238,918		—
Debt securities of government sponsored entities		—		332,051		332,051		332,051		—		—
Federally insured corporate bonds		—		21,454		21,454		21,454		—		—
Money market funds		564,112		20,315		584,427		584,427		—		—
Municipal bonds		3,764		300,817		304,581		—		304,581		—
U.S. Treasury securities		1,000		21,721		22,721		22,721		—		—
Total assets measured at fair value	$	741,835	$	984,011	$	1,725,846	$	960,653	$	743,900	$	21,293

Changes in assets measured at fair value on a recurring basis using significant unobservable inputs (Level 3)

	2011			2010
Balance at beginning of period	$	21,293		$	58,003
Total net realized loss included in investment income and other		(162	)		(290	)
Total net unrealized gain included in other comprehensive income		358			2,790
Sales		—			(12,000	)
Calls by issuers		(9,938	)		(27,210	)
Balance at end of period	$	11,551		$	21,293

Components of the change in auction rate securities

	December 31,
	2011			2010
Proceeds from sale or call of auction rate securities	$	9,938		$	39,210
Total net realized (loss) gain recorded in investment income and other		(162	)		875
Unrealized loss reclassified from accumulated other comprehensive income, included in net realized (loss) gain above		(162	)		(290	)