Marketable Securities - (Tables)

6 Months Ended

Jun. 30, 2014

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

Schedule of marketable securities by category [Table Text Block]

At June 30, 2014 and December 31, 2013, marketable securities are categorized as follows:

	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses		Fair Value
June 30, 2014
Municipal notes and bonds	$	122,292	$	44	$	1	$	122,335
Auction rate securities	475		—		167		308
Total marketable securities	$	122,767	$	44	$	168	$	122,643
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

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, 2014 and December 31, 2013:

	June 30, 2014				December 31, 2013
	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Due within one year	$	110,226	$	110,253	$	81,495	$	81,533
Due after one through five years	12,066		12,082		4,762		4,772
Due after five through ten years	—		—		—		—
Due after ten years	475		308		475		277
Total marketable securities	$	122,767	$	122,643	$	86,732	$	86,582

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, 2014 and December 31, 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
June 30, 2014
Municipal notes and bonds	$	15,122	$	1	$	—	$	—
Auction rate securities	—		—		308		167
Total	$	15,122	$	1	$	308	$	167
December 31, 2013
Municipal notes and bonds	$	16,448	$	2	$	—	$	—
Auction rate securities	—		—		277		198
Total	$	16,448	$	2	$	277	$	198