Investments

Investments classified as available-for-sale, which consist primarily of debt securities, are stated at fair value. Unrealized gains and losses are excluded from earnings and reported as other comprehensive income, net of income tax effects. The cost of investments sold is determined in accordance with the specific identification method, and realized gains and losses are included in net investment income. We periodically assess our available-for-sale investments for other-than-temporary impairment. Any such other-than-temporary impairment loss is recognized as a realized loss, which is recorded through earnings, if related to credit losses.

During the years ended December 31, 2012 and 2011, we recognized no losses from other-than-temporary impairments of our cash equivalents and available-for-sale investments.

We had no noncurrent available-for-sale investments as of December 31, 2012. As of December 31, 2011, we classified $2.1 million as investments available-for-sale-noncurrent because we did not intend to sell and we believed it may take longer than a year for such impaired securities to recover. This classification does not affect the marketability or the valuation of the investments, which are reflected at their market value as of December 31, 2011.

As of December 31, 2012 and 2011, the amortized cost, gross unrealized holding gains and losses, and fair value of our current investments available-for-sale and our investments available-for-sale-noncurrent, after giving effect to other-than-temporary impairments were as follows:



	2012
	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Carrying Value
	(Dollars in millions)
Current:
Asset-backed securities	$	499.7	$	19.6	$	(0.2	)	$	519.1
U.S. government and agencies	25.9		—		—			25.9
Obligations of states and other political subdivisions	819.9		24.2		(2.0		)	842.1
Corporate debt securities	408.4		17.5		(0.5		)	425.4
	$	1,753.9	$	61.3	$	(2.7	)	$	1,812.5



	2011
	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Carrying Value
	(Dollars in millions)
Current:
Asset-backed securities	$	611.9	$	10.6	$	(0.2	)	$	622.3
U.S. government and agencies	32.5		—		—			32.5
Obligations of states and other political subdivisions	498.7		19.5		(0.1		)	518.1
Corporate debt securities	385.0		4.3		(4.2		)	385.1
	$	1,528.1	$	34.4	$	(4.5	)	$	1,558.0
Noncurrent:
Corporate debt securities	$	2.4	$	—	$	(0.3	)	$	2.1

As of December 31, 2012, the contractual maturities of our current investments available-for-sale were as follows:



	Amortized Cost		Estimated Fair Value
Current:	(Dollars in millions)
Due in one year or less	$	34.2	$	34.3
Due after one year through five years	211.6		218.7
Due after five years through ten years	485.3		504.5
Due after ten years	523.1		535.9
Asset-backed securities	499.7		519.1
Total current investments available-for-sale	$	1,753.9	$	1,812.5

Proceeds from sales of investments available-for-sale during 2012 were $1,350.0 million. Gross realized gains and losses during 2012 totaled $37.2 million and $0.5 million, respectively. Proceeds from sales of investments available-for-sale during 2011 were $1,760.3 million. Gross realized gains and losses during 2011 totaled $38.4 million and $5.4 million, respectively.

The following tables show our investments’ fair values and gross unrealized losses for individual securities that have been in a continuous loss position through December 31, 2012 and December 31, 2011. These investments are interest-yielding debt securities of varying maturities. We have determined that the unrealized loss position for these securities is primarily due to market volatility. Generally, in a rising interest rate environment, the estimated fair value of fixed income securities would be expected to decrease; conversely, in a decreasing interest rate environment, the estimated fair value of fixed income securities would be expected to increase. These securities may also be negatively impacted by illiquidity in the market.

The following table shows our current investments' fair values and gross unrealized losses for individual securities in a continuous loss position as of December 31, 2012:



	Less than 12 Months					12 Months or More				Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
	(Dollars in millions)
Asset-backed securities	$	54.9	$	(0.2	)	$	0.1	$	—	$	55.0	$	(0.2	)
U.S. government and agencies	10.1		—			—		—		10.1		—
Obligations of states and other political subdivisions	192.1		(2.0		)	0.2		—		192.3		(2.0		)
Corporate debt securities	45.9		(0.5		)	—		—		45.9		(0.5		)
	$	303.0	$	(2.7	)	$	0.3	$	—	$	303.3	$	(2.7	)

The following table shows the number of our individual securities-current that have been in a continuous loss position at December 31, 2012:



	Less than 12 Months	12 Months or More	Total
Asset-backed securities	25	3	28
U.S. government and agencies	1	—	1
Obligations of states and other political subdivisions	82	1	83
Corporate debt securities	50	—	50
	158	4	162

The following table shows our current investments’ fair values and gross unrealized losses for individual securities that have been in a continuous loss position through December 31, 2011:



	Less than 12 Months					12 Months or More					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
	(Dollars in millions)
Asset-backed securities	$	30.5	$	(0.2	)	$	1.1	$	—		$	31.6	$	(0.2	)
U.S. government and agencies	—		—			—		—			—		—
Obligations of states and other political subdivisions	7.5		—			3.0		(0.1		)	10.5		(0.1		)
Corporate debt securities	149.3		(4.1		)	1.4		(0.1		)	150.7		(4.2		)
	$	187.3	$	(4.3	)	$	5.5	$	(0.2	)	$	192.8	$	(4.5	)

The following table shows our noncurrent investments’ fair values and gross unrealized losses for individual securities that have been in a continuous loss position through December 31, 2011:



	Less than 12 Months					12 Months or More				Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
	(Dollars in millions)
Corporate debt securities	$	2.1	$	(0.3	)	$	—	$	—	$	2.1	$	(0.3	)