The Company's investment policy is consistent with the definition of available-for-sale securities. The Company does not buy and hold securities principally for the purpose of selling them in the near future. The Company's policy is focused on the preservation of capital, liquidity and return. From time to time, the Company may sell certain securities but the objectives are generally not to generate profits on short-term differences in price. The following table summarizes, by major security type, our assets that are measured at fair value on a recurring basis and are categorized using the fair value hierarchy:


	September 30, 2011
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(in thousands)
Cash	$	157,229	$	—	$	—		$	157,229
Level 1 securities (1):
Money market funds		6,532		—		—			6,532
Level 2 securities (3):
Corporate debt securities		116,569		743		(171	)		117,141
Government and agency securities		87,663		740		—			88,403
Asset and mortgage-backed securities		970		59		—			1,029

	$	368,963	$	1,542	$	(171	)	$	370,334

Less: Long-term restricted cash (1)									(4,562	)

Total cash, cash equivalents and short-term investments								$	365,772


	December 31, 2010
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
	(in thousands)
Cash	$	194,146	$	—	$	—		$	194,146
Level 1 securities (2):
Money market funds		4,914		—		—			4,914
Level 2 securities (3):
Corporate debt securities		109,745		1,043		(101	)		110,687
Government and agency securities		42,062		331		(101	)		42,292
Asset and mortgage-backed securities		2,881		168		(140	)		2,909

	$	353,748	$	1,542	$	(342	)		354,948

Less: Long-term restricted cash (2)									(4,561	)

Total cash, cash equivalents and short-term investments								$	350,387

(1)	Includes $2.0 million that is included in cash and cash equivalents and $4.6 million of long-term restricted cash that is included in other non-current assets related to workers compensation deposits.

(2)	Includes $0.4 million that is included in cash and cash equivalents and $4.6 million of long-term restricted cash that is included in other non-current assets related to workers compensation deposits.

(3)	Included in short-term investments.

Fair value is a market-based measurement that should be determined based on the assumptions that market participants would use in pricing an asset or liability. The hierarchy level assigned to each security in the Company's available-for-sale portfolio and cash equivalents is based on its assessment of the transparency and reliability of the inputs used in the valuation of such instrument at the measurement date. The fair value of available-for-sale securities and cash equivalents included in the Level 1 category is based on quoted prices that are readily and regularly available in an active market. The fair value of available-for-sale securities included in the Level 2 category is based on observable inputs, such as quoted prices for similar assets at the measurement date; quoted prices in markets that are not active; or other inputs that are observable, either directly or indirectly. These values were obtained from an independent pricing service and were evaluated using pricing models that vary by asset class and may incorporate available trade, bid and other market information and price quotes from well-established independent pricing vendors and broker-dealers. Our procedures include controls to ensure that appropriate fair values are recorded such as comparing prices obtained from multiple independent sources. See Note 4 for further information regarding the fair value of the Company's 8.50% senior notes.

Because the Company does not intend to sell the investments that are in an unrealized loss position and it is not likely that the Company will be required to sell any investments before recovery of their amortized cost basis, the Company does not consider those investments with an unrealized loss to be other-than-temporarily impaired at September 30, 2011. There were no material other-than-temporary impairments or credit losses related to available-for-sale securities in the three or nine months ended September 30, 2011 and 2010. In addition, there were no material gross realized gains or losses in the three or nine months ended September 30, 2011 and 2010.

The estimated fair value of short-term investments by contractual maturity as of September 30, 2011 is as follows: