Fair Value Measurements (Tables)

6 Months Ended

Jun. 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 June 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	$	144,353	$	13,019	$	157,372	$	—	$	157,372	$	—
Commercial paper	34,720		51,762		86,482		—		86,482		—
Corporate bonds	250		576,063		576,313		—		576,313		—
Debt securities of government sponsored entities	911		219,968		220,879		—		220,879		—
Equity index funds	—		63,850		63,850		63,850		—		—
Money market funds	360,449		60,105		420,554		420,554		—		—
Municipal bonds	8,403		395,293		403,696		—		397,952		5,744
U.S. Treasury securities	—		20,001		20,001		—		20,001		—
Total assets measured at fair value	$	549,086	$	1,400,061	$	1,949,147	$	484,404	$	1,458,999	$	5,744

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

	June 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	515,375		477,648		414,048		400,000