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 investments available-for-sale 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 three and nine months ended September 30, 2015 and 2014, we recognized no losses from other-than-temporary impairments of our cash equivalents and available-for-sale investments.

We classified $20.1 million and $4.6 million as investments available-for-sale-noncurrent as of September 30, 2015 and December 31, 2014, respectively, because we did not intend to sell and we believed it may take longer than one 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 values as of September 30, 2015 and December 31, 2014.

As of September 30, 2015 and December 31, 2014, 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:



	September 30, 2015
	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Carrying Value
	(Dollars in millions)
Current:
Asset-backed securities	$	556.2	$	3.1	$	(1.8	)	$	557.5
U.S. government and agencies	28.1		—		—			28.1
Obligations of states and other political subdivisions	925.1		16.5		(3.0		)	938.6
Corporate debt securities	701.0		2.2		(6.1		)	697.1
	$	2,210.4	$	21.8	$	(10.9	)	$	2,221.3
Noncurrent:
Asset-backed securities	$	0.5	$	—	$	(0.1	)	$	0.4
Obligations of states and other political subdivisions	1.6		—		(0.1		)	1.5
Corporate debt securities	21.7		—		(3.5		)	18.2
	$	23.8	$	—	$	(3.7	)	$	20.1



	December 31, 2014
	Amortized Cost		Gross Unrealized Holding Gains		Gross Unrealized Holding Losses			Carrying Value
	(Dollars in millions)
Current:
Asset-backed securities	$	437.2	$	2.6	$	(1.9	)	$	437.9
U.S. government and agencies	36.5		—		—			36.5
Obligations of states and other political subdivisions	716.7		17.2		(1.7		)	732.2
Corporate debt securities	587.0		2.7		(5.3		)	584.4
	$	1,777.4	$	22.5	$	(8.9	)	$	1,791.0
Noncurrent:
Asset-backed securities	$	0.8	$	—	$	(0.2	)	$	0.6
Corporate debt securities	4.7		—		(0.7		)	4.0
	$	5.5	$	—	$	(0.9	)	$	4.6

As of September 30, 2015, the contractual maturities of our current investments available-for-sale and our investments available-for-sale-noncurrent were as follows:



	Amortized Cost		Estimated Fair Value
Current:	(Dollars in millions)
Due in one year or less	$	42.3	$	42.4
Due after one year through five years	492.1		492.3
Due after five years through ten years	610.5		612.4
Due after ten years	509.3		516.7
Asset-backed securities	556.2		557.5
Total current investments available-for-sale	$	2,210.4	$	2,221.3

	Amortized Cost		Estimated Fair Value
Noncurrent:	(Dollars in millions)
Due after one year through five years	$	10.8	$	9.0
Due after five years through ten years	12.5		10.7
Asset-backed securities	0.5		0.4
Total noncurrent investments available-for-sale	$	23.8	$	20.1

Proceeds from sales of investments available-for-sale during the three and nine months ended September 30, 2015 were $342.0 million and $883.4 million, respectively. Gross realized gains and losses totaled $0.8 million and $0.9 million, respectively, for the three months ended September 30, 2015, and $5.9 million and $3.9 million, respectively, for the nine months ended September 30, 2015. Proceeds from sales of investments available-for-sale during the three and nine months ended September 30, 2014 were $104.6 million and $296.9 million, respectively. Gross realized gains and losses totaled $1.0 million and $0.6 million, respectively, for the three months ended September 30, 2014, and $4.4 million and $1.8 million, respectively, for the nine months ended September 30, 2014.

The following tables show our investments’ fair values and gross unrealized losses for individual securities that have been in a continuous loss position through September 30, 2015 and December 31, 2014. 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 also may be negatively impacted by illiquidity in the market.

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 September 30, 2015:



	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	$	262.2	$	(1.6	)	$	23.9	$	(0.2	)	$	286.1	$	(1.8	)
U.S. government and agencies	12.3		—			—		—			12.3		—
Obligations of states and other political subdivisions	211.2		(2.3		)	17.2		(0.7		)	228.4		(3.0		)
Corporate debt securities	379.4		(5.1		)	27.3		(1.0		)	406.7		(6.1		)
	$	865.1	$	(9.0	)	$	68.4	$	(1.9	)	$	933.5	$	(10.9	)

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 September 30, 2015:



	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	$	—	$	—		$	0.4	$	(0.1	)	$	0.4	$	(0.1	)
Obligations of states and other political subdivisions	—		—			1.5		(0.1		)	1.5		(0.1		)
Corporate debt securities	11.1		(1.9		)	7.1		(1.6		)	18.2		(3.5		)
	$	11.1	$	(1.9	)	$	9.0	$	(1.8	)	$	20.1	$	(3.7	)

The following table shows the number of our individual securities-current that have been in a continuous loss position through September 30, 2015:



	Less than 12 Months	12 Months or More	Total
Asset-backed securities	153	29	182
U.S. government and agencies	1	—	1
Obligations of states and other political subdivisions	149	11	160
Corporate debt securities	343	30	373
	646	70	716

The following table shows the number of our individual securities-noncurrent that have been in a continuous loss position through September 30, 2015:



	Less than 12 Months	12 Months or More	Total
Asset-backed securities	—	1	1
Obligations of states and other political subdivisions	—	1	1
Corporate debt securities	13	11	24
	13	13	26

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, 2014:



	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	$	149.3	$	(0.5	)	$	112.5	$	(1.4	)	$	261.8	$	(1.9	)
U.S. government and agencies	20.7		—			—		—			20.7		—
Obligations of states and other political subdivisions	37.3		(0.1		)	104.8		(1.6		)	142.1		(1.7		)
Corporate debt securities	299.1		(3.9		)	56.0		(1.4		)	355.1		(5.3		)
	$	506.4	$	(4.5	)	$	273.3	$	(4.4	)	$	779.7	$	(8.9	)

The following table shows our noncurrent investments' fair value and gross unrealized losses for our individual securities that have been in a continuous loss position through December 31, 2014:



	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	$	—	$	—		$	0.6	$	(0.2	)	$	0.6	$	(0.2	)
Corporate debt securities	4.0		(0.7		)	—		—			4.0		(0.7		)
	$	4.0	$	(0.7	)	$	0.6	$	(0.2	)	$	4.6	$	(0.9	)