Fair Value Measurements (Tables)

6 Months Ended

Jun. 30, 2011

Fair Value Measurements [Abstract]

Assets measured at fair value on a recurring basis

							Fair Value Measurements at Reporting Date Using
							Quoted Prices in				Significant
	Fair Value		Fair Value of				Active Markets for		Significant Other		Unobservable
	of Cash		Available-for-		Total Fair		Identical Assets		Observable Inputs		Inputs
	Equivalents		Sale Securities		Value		(Level 1)		(Level 2)		(Level 3)
Auction rate securities	$	—	$	15,672	$	15,672	$	—	$	—	$	15,672
Certificates of deposit		135,653		7,002		142,655		—		142,655		—
Commercial paper		1,000		51,262		52,262		—		52,262		—
Corporate bonds		—		346,179		346,179		—		346,179		—
Debt securities of government sponsored entities		13,000		375,444		388,444		388,444		—		—
Equity index funds		—		16,217		16,217		16,217		—		—
Federally insured corporate bonds		—		21,230		21,230		21,230		—		—
Money market funds		427,168		23,791		450,959		450,959		—		—
Municipal bonds		—		361,755		361,755		—		361,755		—
U.S. Treasury securities		—		34,498		34,498		34,498		—		—
Total assets measured at fair value	$	576,821	$	1,253,050	$	1,829,871	$	911,348	$	902,851	$	15,672

							Fair Value Measurements at Reporting Date Using
							Quoted Prices in				Significant
	Fair Value		Fair Value of				Active Markets for		Significant Other		Unobservable
	of Cash		Available-for-		Total Fair		Identical Assets		Observable Inputs		Inputs
	Equivalents		Sale Securities		Value		(Level 1)		(Level 2)		(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)

	Three Months Ended June 30,						Six Months Ended June 30,
	2011			2010			2011			2010
Balance at beginning of period	$	17,394		$	50,522		$	21,293		$	58,003
Total net realized loss included in investment income and other		—			(211	)		—			(290	)
Total net unrealized (loss) gain included in other comprehensive income		(47	)		1,073			279			1,541
Sales		—			(9,050	)		—			(12,000	)
Calls by issuers		(1,675	)		(11,290	)		(5,900	)		(16,210	)
Balance at end of period	$	15,672		$	31,044		$	15,672		$	31,044

Components of the change in auction rate securities

	Three Months Ended					Six Months Ended
	June 30,					June 30,
	2011		2010			2011		2010
Proceeds from sale or call of auction rate securities	$	1,675	$	20,340		$	5,900	$	28,210
Total net realized gain included in investment income and other		—		674			—		875
Net unrealized loss reclassified from accumulated other comprehensive income, included in realized gain above		—		(210	)		—		(290	)