Marketable Securities (Tables)

3 Months Ended

Mar. 31, 2012

Marketable Securities [Abstract]

Marketable Securities, Based on Contractual Maturity Dates

The following tables summarize the amortized cost basis of debt securities included in marketable securities, the aggregate fair value of those securities, and gross unrealized gains and losses on those securities at March 31, 2012 and December 31, 2011.

	Amortized	Fair	Unrealized
At March 31, 2012	Cost Basis	Value	Gains	(Losses)	Net
Unrestricted
Maturities within one year:
U.S. government obligations	$10,017	$10,049	$32		$32
U.S. government guaranteed corporate            bonds	15,285	15,324	39		39
U.S. government guaranteed collateralized mortgage obligations	188	188
Municipal bonds	12,147	12,152	6	$(1)	5
	37,637	37,713	77	(1)	76
Maturities after one year through five years:
U.S. government obligations	250,719	251,004	387	(102)	285
Mortgage-backed securities	103	30		(73)	(73)
	250,822	251,034	387	(175)	212
Maturities after five years through ten years:
Mortgage-backed securities	162	93		(69)	(69)
	288,621	288,840	464	(245)	219
Restricted
Maturities within one year:
U.S. government obligations	3,330	3,335	5		5
Maturities after one year through five years:
U.S. government obligations	4,724	4,728	8	(4)	4
	8,054	8,063	13	(4)	9
	$296,675	$296,903	$477	$(249)	$228

	Amortized			Fair		Unrealized
At December 31, 2011	Cost Basis			Value		Gains	(Losses)		Net
Unrestricted
Maturities within one year:
U.S. government obligations		$12,025	$12,067		$42				$42
U.S. government guaranteed corporate bonds		15,263	15,316		53				53
U.S. government guaranteed collateralized mortgage obligations		623	622					$(1)	(1)
Municipal bonds		15,314	15,326		13			(1)	12
		43,225	43,331		108			(2)	106
Maturities after one year through five years:
U.S. government obligations		272,433	272,752		400			(81)	319
Mortgage-backed securities		104	28					(76)	(76)
		272,537	272,780		400			(157)	243
Maturities after five years through ten years:
Mortgage-backed securities		164	87					(77)	(77)
		315,926	316,198		508			(236)	272
Restricted
Maturities within one year:
U.S. government obligations		3,347	3,357		10				10
Maturities after one year through five years:
U.S. government obligations		2,572	2,583		11				11
		5,919	5,940		21				21
		$321,845	$322,138		$529			$(236)	$293

Fair Value and Unrealized Losses of Marketable Securities

The following table shows the fair value of the Company's marketable securities that have unrealized losses and that are deemed to be only temporarily impaired, aggregated by investment category and length of time that the individual securities have been in a continuous unrealized loss position, at March 31, 2012 and December 31, 2011.

	Less than 12 Months		12 Months or Greater		Total
At March 31, 2012	Fair Value	Unrealized Loss	Fair Value	Unrealized Loss	Fair Value	Unrealized Loss
Unrestricted
U.S. government obligations	$261,053	$(102)			$261,053	$(102)
Municipal bonds	12,152	(1)			12,152	(1)
Equity security	3,611	(434)			3,611	(434)
Mortgage-backed securities			$123	$(142)	123	(142)
	276,816	(537)	123	(142)	276,939	(679)
Restricted
U.S. government obligations	2,417	(4)			2,417	(4)
	2,417	(4)			2,417	(4)
	$279,233	$(541)	$123	$(142)	$279,356	$(683)

	Less than 12 Months		12 Months or Greater		Total
At December 31, 2011	Fair Value	Unrealized Loss	Fair Value	Unrealized Loss	Fair Value	Unrealized Loss
Unrestricted
U.S. government obligations	$103,529	$(81)			$103,529	$(81)
U.S. government guaranteed collateralized mortgage   obligations	623	(1)			623	(1)
Municipal bonds	4,603	(1)			4,603	(1)
Equity security	3,019	(1,025)			3,019	(1,025)
Mortgage-backed securities			$116	$(152)	116	(152)
	$111,774	$(1,108)	$116	$(152)	$111,890	$(1,260)

Fair Value, Assets Measured on a Recurring Basis

The Company's assets that are measured at fair value on a recurring basis, at March 31, 2012 and December 31, 2011, were as follows:

		Fair Value Measurements at Reporting Date Using
	Fair Value	Quoted Prices in Active Markets for Identical Assets (Level 1)	Significant Other Observable Inputs (Level 2)	Significant Unobservable Inputs (Level 3)
At March 31, 2012
Unrestricted
Available-for-sale marketable securities:
U.S. government obligations	$261,053		$261,053
U.S. government guaranteed corporate bonds	15,324		15,324
U.S. government guaranteed collateralized mortgage obligations	188		188
Municipal bonds	12,152		12,152
Mortgage-backed securities	123		123
Equity security	3,611	$3,611
	292,451	3,611	288,840
Restricted
Available-for-sale marketable securities:
U.S. government obligations	8,063		8,063
	$300,514	$3,611	$296,903

				Fair Value Measurements at Reporting Date Using
	Fair Value			Quoted Prices in Active Markets for Identical Assets (Level 1)	Significant Other Observable Inputs (Level 2)	Significant Unobservable Inputs (Level 3)
At December 31, 2011
Unrestricted
Available-for-sale marketable securities:
U.S. government obligations		$284,819			$284,819
U.S. government guaranteed corporate bonds		15,316			15,316
U.S. government guaranteed collateralized mortgage obligations		622			622
Municipal bonds		15,326			15,326
Mortgage-backed securities		115			115
Equity security		3,019		$3,019
		319,217		3,019	316,198
Restricted
Available-for-sale marketable   securities:
U.S. government obligations			5,940		5,940
			$325,157	$3,019	$322,138