Investments (Tables)

9 Months Ended

12 Months Ended

Sep. 30, 2011

Dec. 31, 2010

Investments

Available-For-Sale Investments, Including Accrued Interest

	September 30, 2011
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Corporate debt securities	$	325,872	$	4,638	$	(848	)	$	329,662
Residential mortgage-backed securities		90,422		1,449		(41	)		91,830
Government-sponsored enterprise securities		15,251		62		—			15,313
Asset-backed securities		65,257		81		(6	)		65,332
Subtotal - Marketable securities		496,802		6,230		(895	)		502,137
Restricted cash and cash equivalents		8,844		—		—			8,844
U.S. Treasury and agencies		1,300		5		—			1,305
Corporate debt securities		50,139		337		(192	)		50,284
Residential mortgage-backed securities		7,768		44		(11	)		7,801
Government-sponsored enterprise securities		8,544		18		(2	)		8,560
Asset-backed securities		3,122		5		—			3,127
Subtotal - Restricted investments		79,717		409		(205	)		79,921
Total	$	576,519	$	6,639	$	(1,100	)	$	582,058

	December 31, 2010
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Corporate debt securities	$	125,708	$	1,655	$	(19	)	$	127,344
Residential mortgage-backed securities		53,944		787		(13	)		54,718
Government-sponsored enterprise securities		86,905		61		—			86,966
Asset-backed securities		12,983		5		—			12,988
Subtotal - Marketable securities		279,540		2,508		(32	)		282,016
Corporate debt securities		248,500		3,611		(881	)		251,230
Residential mortgage-backed securities		79,605		1,161		(20	)		80,746
Government-sponsored enterprise securities		25,402		3		(120	)		25,285
Asset-backed securities		58,822		84		(2	)		58,904
Subtotal - Marketable securities, non-current		412,329		4,859		(1,023	)		416,165
U.S. Treasury and agencies		1,302		10		—			1,312
Restricted cash and cash equivalents		7,455		—		—			7,455
Corporate debt securities		45,931		620		(29	)		46,522
Residential mortgage-backed securities		6,368		128		—			6,496
Government-sponsored enterprise securities		13,237		72		(6	)		13,303
Asset-backed securities		4,412		10		—			4,422
Subtotal - Restricted investments		78,705		840		(35	)		79,510
Total	$	770,574	$	8,207	$	(1,090	)	$	777,691

Gross Unrealized Losses And Fair Value Of Investments With Unrealized Losses

	December 31, 2010
	Loss Position for Less Than Twelve Months					Loss Position for Greater Than Twelve Months					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
Corporate debt securities	$	35,432	$	(18	)	$	1,536	$	(1	)	$	36,968	$	(19	)
Residential mortgage-backed securities		54,718		(13	)		—		—			54,718		(13	)
Asset-backed securities		3,286		—			—		—			3,286		—
Subtotal - Marketable securities		93,436		(31	)		1,536		(1	)		94,972		(32	)
Corporate debt securities		56,992		(881	)		—		—			56,992		(881	)
Residential mortgage-backed securities		80,746		(20	)		—		—			80,746		(20	)
Government-sponsored enterprise securities		20,237		(120	)		—		—			20,237		(120	)
Asset-backed securities		8,400		(2	)		—		—			8,400		(2	)
Subtotal - Marketable securities, non-current		166,375		(1,023	)		—		—			166,375		(1,023	)
Corporate debt securities		7,110		(29	)		—		—			7,110		(29	)
Government-sponsored enterprise securities		1,502		(6	)		—		—			1,502		(6	)
Subtotal - Restricted investments		8,612		(35	)		—		—			8,612		(35	)
Total	$	268,423	$	(1,089	)	$	1,536	$	(1	)	$	269,959	$	(1,090	)

Maturities Of Marketable Securities And Restricted Investments

	Marketable Securities				Restricted Investments
	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Less than one year	$	120,284	$	121,534	$	34,628	$	34,715
Due in year two through year three		307,669		310,586		40,719		40,876
Due in year four through year five		47,776		48,644		4,182		4,140
Due after five years		21,073		21,373		188		190
Total	$	496,802	$	502,137	$	79,717	$	79,921

Realized Gains And Losses On Securities Sold Before Maturity And Respective Net Proceeds

	Three months ended September 30,						Nine months ended September 30,
	2011			2010			2011			2010
Proceeds on sale of investments	$	96,319		$	111,421		$	422,226		$	582,015
Realized gains		341			140			521			1,618
Realized losses		(303	)		(512	)		(1,135	)		(1,379	)