Investments

The following tables summarize our investments as of the dates indicated:



	March 31, 2013
	Amortized		Gross Unrealized				Estimated Fair
	Cost		Gains		Losses		Value
	(In thousands)
Corporate debt securities	$	198,265	$	441	$	139	$	198,567
Government-sponsored enterprise securities (GSEs)	27,372		27		—		27,399
Municipal securities	75,216		348		153		75,411
U.S. treasury notes	31,894		44		—		31,938
Certificates of deposit	8,617		14		—		8,631
Subtotal - current investments	341,364		874		292		341,946
Auction rate securities	14,500		—		900		13,600
	$	355,864	$	874	$	1,192	$	355,546

	December 31, 2012
	Amortized		Gross Unrealized				Estimated Fair
	Cost		Gains		Losses		Value
	(In thousands)
Corporate debt securities	$	190,545	$	528	$	65	$	191,008
GSEs	29,481		45		1		29,525
Municipal securities	75,909		185		246		75,848
U.S. treasury notes	35,700		42		2		35,740
Certificates of deposit	10,715		9		—		10,724
Subtotal - current investments	342,350		809		314		342,845
Auction rate securities	14,650		—		1,231		13,419
	$	357,000	$	809	$	1,545	$	356,264

The contractual maturities of our investments as of March 31, 2013 are summarized below:



	Cost		Estimated Fair Value
	(In thousands)
Due in one year or less	$	173,871	$	174,145
Due one year through five years	167,493		167,801
Due after ten years	14,500		13,600
	$	355,864	$	355,546

Gross realized gains and gross realized losses from sales of available-for-sale securities are calculated under the specific identification method and are included in investment income. Net realized investment gains for the three months ended March 31, 2013, and 2012 were $94,000 and $64,000 respectively.

We monitor our investments for other-than-temporary impairment. For investments other than our auction rate securities, discussed below, we have determined that unrealized gains and losses at March 31, 2013, and December 31, 2012, are temporary in nature, because the change in market value for these securities has resulted from fluctuating interest rates, rather than a deterioration of the credit worthiness of the issuers. So long as we hold these securities to maturity, we are unlikely to experience gains or losses. In the event that we dispose of these securities before maturity, we expect that realized gains or losses, if any, will be immaterial.

The following tables segregate those available-for-sale investments that have been in a continuous loss position for less than 12 months, and those that have been in a loss position for 12 months or more as of March 31, 2013.



	In a Continuous Loss Position for Less than 12 Months					In a Continuous Loss Position for 12 Months or More
	Estimated Fair Value		Unrealized Losses		Total Number of Securities	Estimated Fair Value		Unrealized Losses		Total Number of Securities
	(Dollars in thousands)
Corporate debt securities	$	52,264	$	139	28	$	—	$	—	—
Municipal securities	21,440		153		37	—		—		—
Auction rate securities	—		—		—	13,600		900		19
	$	73,704	$	292	65	$	13,600	$	900	19

The following table segregates those available-for-sale investments that have been in a continuous loss position for less than 12 months, and those that have been in a loss position for 12 months or more as of December 31, 2012.



	In a Continuous Loss Position for Less than 12 Months					In a Continuous Loss Position for 12 Months or More
	Estimated Fair Value		Unrealized Losses		Total Number of Securities	Estimated Fair Value		Unrealized Losses		Total Number of Securities
	(Dollars in thousands)
Corporate debt securities	$	44,457	$	65	23	$	—	$	—	—
Municipal securities	35,223		246		43	—		—		—
GSEs	5,004		1		1	—		—		—
U.S. treasury notes	4,511		2		5	—		—		—
Auction rate securities	—		—		—	13,419		1,231		21
	$	89,195	$	314	72	$	13,419	$	1,231	21

Auction Rate Securities

Due to events in the credit markets, the auction rate securities held by us experienced failed auctions beginning in the first quarter of 2008, and such auctions have not resumed. Therefore, quoted prices in active markets have not been available since early 2008. Our investments in auction rate securities are collateralized by student loan portfolios guaranteed by the U.S. government, and the range of maturities for such securities is from 18 years to 34 years. Considering the relative insignificance of these securities when compared with our liquid assets and other sources of liquidity, we have no current intention of selling these securities nor do we expect to be required to sell these securities before a recovery in their cost basis. For this reason, and because the decline in the fair value of the auction securities was not due to the credit quality of the issuers, we do not consider the auction rate securities to be other-than-temporarily impaired at March 31, 2013. At the time of the first failed auctions during first quarter 2008, we held a total of $82.1 million in auction rate securities at par value; since that time, we have settled $67.6 million of these instruments at par value.

For the three months ended March 31, 2013, and 2012, we recorded pretax unrealized gains of $0.3 million and $0.1 million, respectively, to accumulated other comprehensive income for the changes in their fair value. Any future fluctuation in fair value related to these instruments that we deem to be temporary, including any recoveries of previous write-downs, would be recorded to accumulated other comprehensive income. If we determine that any future valuation adjustment was other-than-temporary, we would record a charge to earnings as appropriate.