Marketable Securities - (Tables)

6 Months Ended

Jun. 30, 2013

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

Schedule of marketable securities by category [Table Text Block]

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

	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Fair Value
June 30, 2013
Municipal notes and bonds	$	90,199	$	40	$	(8	)	$	90,231
Corporate bonds	500		—		—			500
Auction rate securities	475		—		(173		)	302
Total marketable securities	$	91,174	$	40	$	(181	)	$	91,033
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 June 30, 2013 and December 31, 2012:

	June 30, 2013				December 31, 2012
	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Due within one year	$	78,692	$	78,723	$	57,367	$	57,390
Due after one through five years	9,731		9,732		7,016		7,022
Due after five through ten years	738		738		205		205
Due after ten years	2,013		1,840		475		346
Total marketable securities	$	91,174	$	91,033	$	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 June 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
June 30, 2013
Municipal notes and bonds	$	11,175	$	(8	)	$	—	$	—
Auction rate securities	—		—			302		(173		)
Total	$	11,175	$	(8	)	$	302	$	(173	)
December 31, 2012
Municipal notes and bonds	$	9,037	$	(7	)	$	—	$	—
Auction rate securities	—		—			346		(129		)
Total	$	9,037	$	(7	)	$	346	$	(129	)