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

Cash and cash equivalents, short-term investments, and restricted cash equivalents and investments as of March 31, 2012, consisted of the following (in thousands):


	Amortized Cost		Estimated Fair Value
Cash and cash equivalents:
Cash	$	53,435	$	53,435
Money market mutual funds		11,347		11,347
Corporate notes and bonds		18,550		18,550

Total cash and cash equivalents		83,332		83,332

Short-term investments:
Corporate notes and bonds		46,484		46,524
U.S. government agency securities		37,111		37,157

Total short-term investments		83,595		83,681

Total cash, cash equivalents and short-term investments	$	166,927	$	167,013

Restricted cash equivalents and investments	$	10,173	$	10,173

Cash and cash equivalents, short-term investments, and restricted cash equivalents and investments as of December 31, 2011 consisted of the following (in thousands):


	Amortized Cost		Estimated Fair Value
Cash and cash equivalents:
Cash	$	79,092	$	79,092
Money market mutual funds		6,544		6,544
Corporate notes and bonds		20,697		20,697

Total cash and cash equivalents		106,333		106,333

Short-term investments:
Corporate notes and bonds		39,309		39,254
U.S. Government agency securities		39,413		39,485

Total short-term investments		78,722		78,739

Total cash, cash equivalents, and short-term investments	$	185,055	$	185,072

Restricted cash equivalents and investments	$	10,168	$	10,168

As of March 31, 2012, and December 31, 2011, restricted cash equivalents and investments represented cash equivalents and short-term investments pledged as collateral against a letter of credit in connection with lease agreements.

Realized gains or losses on sales of available-for-sale securities for the quarters ended March 31, 2012 and 2011, were not significant.

Gross unrealized gains and gross unrealized losses on short-term investment securities as of March 31, 2012 and December 31, 2011 were not significant.

Investments with remaining contractual maturities of five years or less are classified as short-term based on their highly liquid nature and because such marketable securities represent the investment of cash that is available for current operations. The contractual maturities of short-term investments as of March 31, 2012, were as follows (in thousands):


	Estimated Fair Value
Within one year	$	53,521
Between one year and five years		30,160

Total short-term investments	$	83,681