Marketable Securities - (Tables)

9 Months Ended

Sep. 30, 2013

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

Schedule of marketable securities by category [Table Text Block]

At September 30, 2013 and December 31, 2012, marketable securities are categorized as follows:

	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Fair Value
September 30, 2013
Municipal notes and bonds	$	73,975	$	47	$	(3	)	$	74,019
Corporate bonds	501		—		—			501
Auction rate securities	475		—		(184		)	291
Total marketable securities	$	74,951	$	47	$	(187	)	$	74,811
December 31, 2012
Municipal notes and bonds	$	64,088	$	36	$	(7	)	$	64,117
Corporate bonds	500		—		—			500
Auction rate securities	475		—		(129		)	346
Total marketable securities	$	65,063	$	36	$	(136	)	$	64,963

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 September 30, 2013 and December 31, 2012:

	September 30, 2013				December 31, 2012
	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Due within one year	$	65,676	$	65,710	$	57,367	$	57,390
Due after one through five years	8,800		8,810		7,016		7,022
Due after five through ten years	—		—		205		205
Due after ten years	475		291		475		346
Total marketable securities	$	74,951	$	74,811	$	65,063	$	64,963

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 September 30, 2013 and December 31, 2012:  

	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
September 30, 2013
Municipal notes and bonds	$	4,486	$	(3	)	$	—	$	—
Auction rate securities	—		—			291		(184		)
Total	$	4,486	$	(3	)	$	291	$	(184	)
December 31, 2012
Municipal notes and bonds	$	9,037	$	(7	)	$	—	$	—
Auction rate securities	—		—			346		(129		)
Total	$	9,037	$	(7	)	$	346	$	(129	)