Note 6. Cash, Cash Equivalents, Short-Term Investments, Restricted Cash Equivalents and Investments

Cash, cash equivalents, short-term investments, and restricted cash equivalents as of June 30, 2011, consist of the following (in thousands):


	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Cash and cash equivalents:
Cash	$	75,057	$	0	$	0		$	75,057
Money market mutual funds		31,075		0		0			31,075
Corporate notes and bonds		126,398		0		0			126,398
U.S. government agency securities		4,200		0		0			4,200

Total cash and cash equivalents		236,730		0		0			236,730

Short-term investments:
Corporate notes and bonds		52,411		163		(10	)		52,564
U.S. government agency securities		38,506		80		(8	)		38,578

Total short-term investments		90,917		243		(18	)		91,142

Total cash, cash equivalents and short-term investments	$	327,647	$	243	$	(18	)	$	327,872

Restricted cash equivalents and investments	$	10,141	$	0	$	0		$	10,141

Cash, cash equivalents, short-term investments, and restricted cash equivalents as of December 31, 2010 consist of the following (in thousands):


	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Cash and cash equivalents:
Cash	$	66,986	$	0	$	0		$	66,986
Money market mutual funds		44,348		0		0			44,348
Corporate notes and bonds		120,984		0		0			120,984
U.S. government agency securities		3,700		0		0			3,700

Total cash and cash equivalents		236,018		0		0			236,018

Short-term investments:
Corporate notes and bonds		75,962		221		(26	)		76,157
U.S. government agency securities		22,126		23		(3	)		22,146

Total short-term investments		98,088		244		(29	)		98,303

Total cash, cash equivalents and short-term investments	$	334,106	$	244	$	(29	)	$	334,321

Restricted cash equivalents and investments	$	10,000	$	0	$	0		$	10,000

At June 30, 2011, and December 31, 2010, restricted cash equivalents and investments represent cash equivalents and short-term investments pledged as collateral against a letter of credit for a total of $10.1 million in connection with lease agreements.

Realized gains or losses on sales of available-for-sale securities for the quarters and six month period ended June 30, 2011 and 2010, were not significant.

Changes in estimated fair values of short-term investments are primarily related to changes in interest rates and are considered to be temporary in nature.

The contractual maturities of short-term investments at June 30, 2011, are as follows (in thousands):


	Amortized Cost		Estimated Fair Value
Within one year	$	38,860	$	38,915
Between one year and five years		52,057		52,227

Total short-term investments	$	90,917	$	91,142