Marketable Securities (Tables)

3 Months Ended

Mar. 31, 2012

Schedule of Available-for-sale Securities [Line Items]

Schedule of marketable securities by category [Table Text Block]

At March 31, 2012 and December 31, 2011, marketable securities are categorized as follows:

	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Fair Value
March 31, 2012
Municipal notes and bonds	$	84,253	$	70	$	(10	)	$	84,313
Auction rate securities	500		—		(164		)	336
Total marketable securities	$	84,753	$	70	$	(174	)	$	84,649
December 31, 2011
Municipal notes and bonds	$	70,475	$	60	$	(10	)	$	70,525
Auction rate securities	500		—		(137		)	363
Total marketable securities	$	70,975	$	60	$	(147	)	$	70,888

Schedule of marketable securities classified by contractual maturity date [Table Text Block]

The amortized cost and estimated fair value of marketable securities classified by the maturity date listed on the security, regardless of the Condensed Consolidated Balance Sheet classification, is as follows at March 31, 2012 and December 31, 2011:

	March 31, 2012				December 31, 2011
	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Due within one year	$	72,336	$	72,376	$	59,469	$	59,509
Due after one through five years	11,292		11,317		10,587		10,599
Due after five through ten years	521		517		314		312
Due after ten years	604		439		605		468
Total marketable securities	$	84,753	$	84,649	$	70,975	$	70,888

Schedule of marketable securities in unrealized loss positions [Table Text Block]

The following table summarizes the estimated fair value and gross unrealized holding losses of marketable securities, aggregated by investment instrument and period of time in an unrealized loss position at March 31, 2012 and December 31, 2011:  

	In Unrealized Loss Position For Less Than 12 Months					In Unrealized Loss Position For Greater Than 12 Months
	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
March 31, 2012
Municipal notes and bonds	$	14,835	$	(10	)	$	—	$	—
Auction rate securities	—		—			336		(164		)
Total	$	14,835	$	(10	)	$	336	$	(164	)
December 31, 2011
Municipal notes and bonds	7,291		(10		)	—		—
Auction rate securities	—		—			363		(137		)
Total	$	7,291	$	(10	)	$	363	$	(137	)