Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2012

Fair Value Disclosures [Abstract]

Assets measured at fair value on a recurring basis

The Company's assets measured at fair value on a recurring basis at September 30, 2012 were as follows (dollars in thousands):

							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)
Certificates of deposit	$	87,744	$	13,024	$	100,768	$	—	$	100,768	$	—
Commercial paper	61,791		61,433		123,224		—		123,224		—
Corporate bonds	—		599,505		599,505		—		599,505		—
Debt securities of government sponsored entities	8,323		146,157		154,480		—		154,480		—
Equity index funds	—		72,675		72,675		72,675		—		—
Money market funds	539,234		87,752		626,986		626,986		—		—
Municipal bonds	8,220		498,723		506,943		—		500,987		5,956
U.S. Treasury securities	—		14,810		14,810		—		14,810		—
Total assets measured at fair value	$	705,312	$	1,494,079	$	2,199,391	$	699,661	$	1,493,774	$	5,956

The Company's assets measured at fair value on a recurring basis at December 31, 2011 were as follows (dollars in thousands):

							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)
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(1)	—		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		410,577		413,698		—		402,147		11,551
U.S. Treasury securities(1)	—		26,124		26,124		—		26,124		—
Total assets measured at fair value	$	539,512	$	1,640,536	$	2,180,048	$	460,667	$	1,707,830	$	11,551

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(1) The table has been corrected to reflect debt securities of government sponsored entities and U.S. Treasury securities as Level 2 within the fair value hierarchy. Previously, these instruments were reflected as Level 1.

Fair value and carrying value of long-term debt

As of September 30, 2012 and December 31, 2011, the fair values and carrying values of these instruments were as follows (dollars in thousands):

	September 30, 2012				December 31, 2011
	Fair Value		Carrying Value		Fair Value		Carrying Value
2.0% Convertible Senior Notes	$	—	$	—	$	371,005	$	256,995
7.5% Senior Notes	555,750		477,558		414,048		400,000