Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2013

Marketable Securities [Abstract]

Available-for-sale Securities [Table Text Block]

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

	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Fair Value
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
December 31, 2013
Municipal notes and bonds	$	86,257	$	50	$	(2	)	$	86,305
Auction rate securities	475		—		(198		)	277
Total marketable securities	$	86,732	$	50	$	(200	)	$	86,582

Investments 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 Consolidated Balance Sheet classification, is as follows at December 31, 2012 and 2013:

	December 31, 2012				December 31, 2013
	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Due within one year	$	57,367	$	57,390	$	78,909	$	78,948
Due after one through five years	7,016		7,022		5,811		5,821
Due after five through ten years	205		205		—		—
Due after ten years	475		346		2,011		1,813
Total marketable securities	$	65,063	$	64,963	$	86,731	$	86,582

Schedule of Unrealized Loss on Investments [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 December 31, 2012 and 2013.

	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
December 31, 2012
Municipal notes and bonds	$	9,037	$	(7	)	$	—	$	—
Tax-free auction rate securities	—		—			346		(129		)
Total marketable securities	$	9,037	$	(7	)	$	346	$	(129	)
December 31, 2013
Municipal notes and bonds	$	16,448	$	(2	)	$	—	$	—
Tax-free auction rate securities	—		—			475		(198		)
Total marketable securities	$	16,448	$	(2	)	$	475	$	(198	)