Investments in Marketable Securities (Tables)

6 Months Ended

Jun. 30, 2012

Investments in Marketable Securities [Abstract]

Fair value of available-for-sale investments by types and classes of security

At June 30, 2012	Amortized     Cost Basis		Other-than-     temporary Impairments		Gross Unrealized     Holding Gains		Gross Unrealized     Holding Losses		Fair Value
Available-for-sale:
Debt instruments – Municipal debt obligations	$	2,772	$	—	$	—	$	—	$	2,772
Certificates of deposit		1,000		—		—		—		1,000
	$	3,772	$	—	$	—	$	—	$	3,772

At December 31, 2011	Amortized     Cost Basis		Other-than-     temporary Impairments		Gross Unrealized     Holding Gains		Gross Unrealized     Holding Losses			Fair Value
Available-for-sale:
Debt instruments – Corporate debt obligations	$	37,392	$	—	$	3	$	(1	)	$	37,394
Debt instruments – Municipal debt obligations		6,224		—		—		—			6,224
Certificates of deposit		1,000		—		—		—			1,000
	$	44,616	$	—	$	3	$	(1	)	$	44,618

Investments by contractual maturity

	June 30, 2012				December 31, 2011
	Cost		Fair Value		Cost		Fair Value
Due or callable in one year or less	$	3,772	$	3,772	$	44,616	$	44,618
Due after one year	$	—	$	—	$	—	$	—