Fair Value (Tables)

12 Months Ended

Dec. 31, 2010

Fair Value [Abstract]

Fair Value, Assets Measured On Recurring Basis

			Fair Value Measurements Using
	Fair Value		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant  Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	(in thousands)
December 31, 2010
Cash equivalents	$	1,606,592	$	1,606,592	$	0	$	0
Debt securities:
U.S. Treasury and other U.S. government corporations and agencies:
U.S. Treasury and agency obligations		711,613		0		711,613		0
Mortgage-backed securities		1,663,179		0		1,663,179		0
Tax-exempt municipal securities		2,433,334		0		2,381,528		51,806
Mortgage-backed securities:
Residential		55,887		0		55,887		0
Commercial		321,031		0		321,031		0
Asset-backed securities		149,751		0		148,545		1,206
Corporate debt securities		3,032,311		0		3,025,097		7,214
Redeemable preferred stock		5,333		0		0		5,333
Total debt securities		8,372,439		0		8,306,880		65,559
Securities lending invested collateral		49,636		24,639		24,997		0
Total invested assets	$	10,028,667	$	1,631,231	$	8,331,877	$	65,559
December 31, 2009
Cash equivalents	$	1,507,490	$	1,507,490	$	0	$	0
Debt securities:
U.S. Treasury and other U.S. government corporations and agencies:
U.S. Treasury and agency obligations		1,009,352		0		1,009,352		0
Mortgage-backed securities		1,688,663		0		1,688,663		0
Tax-exempt municipal securities		2,224,041		0		2,155,227		68,814
Mortgage-backed securities:
Residential		95,412		0		95,412		0
Commercial		279,626		0		279,626		0
Asset-backed securities		107,188		0		105,060		2,128
Corporate debt securities		2,079,568		0		2,071,087		8,481
Redeemable preferred stock		13,300		0		0		13,300
Total debt securities		7,497,150		0		7,404,427		92,723
Securities lending invested collateral		119,586		53,569		66,017		0
Total invested assets	$	9,124,226	$	1,561,059	$	7,470,444	$	92,723

Fair Value, Assets Measured On Recurring Basis, Unobservable Input Reconciliation

	For the year ended December 31,
	2010									2009
	Auction Rate Securities			Privates and Venture Capital			Total			Auction Rate Securities			Privates and Venture Capital			Total
	(in thousands)
Beginning balance at January 1	$	68,814		$	23,909		$	92,723		$	73,654		$	18,272		$	91,926
Total gains or losses:
Realized in earnings		16			6,244			6,260			16			74			90
Unrealized in other comprehensive income		1,901			(4,426	)		(2,525	)		269			4,382			4,651
Purchases, sales, issuances, and settlements, net		(18,925	)		(11,974	)		(30,899	)		(5,125	)		(2,102	)		(7,227	)
Transfers into Level 3		0			0			0			0			3,283			3,283
Balance at December 31	$	51,806		$	13,753		$	65,559		$	68,814		$	23,909		$	92,723