2. INVESTMENTS

We classify all of our short-term investments as available-for-sale. We carry these at fair value and report unrealized gains and losses, net of taxes, in Accumulated other comprehensive loss (income), which is a separate component of shareholders’ equity in our Condensed Consolidated Balance Sheets. These unrealized gains and losses are also reflected in our Condensed Consolidated Statements of Comprehensive Income and Condensed Consolidated Statements of Shareholders’ Equity. Cost, gains, and losses are determined using the specific identification method.

Investments consisted of the following as of March 31, 2015:


			Unrealized		Unrealized			Fair
	Cost Basis		Gains		Losses			Value
	(Thousands of dollars)
Investments:
Money market mutual funds	$	18,055	$	—	$	—		$	18,055
U.S. Government agencies		8,007		6		(1	)		8,012
Municipal bonds and notes		1,500		1		—			1,501
Corporate bonds and notes		177,511		23		(137	)		177,397

Subtotal		205,073		30		(138	)		204,965
Deferred compensation plan assets included in other assets		2,475		—		—			2,475

Total	$	207,548	$	30	$	(138	)	$	207,440

Investments consisted of the following as of December 31, 2014:


			Unrealized		Unrealized			Fair
	Cost Basis		Gains		Losses			Value
	(Thousands of dollars)
Investments:
Money market mutual funds	$	68,612	$	—	$	—		$	68,612
Municipal bonds and notes		1,500		2		—			1,502
Corporate bonds and notes		130,864		19		(268	)		130,615

Subtotal		200,976		21		(268	)		200,729
Deferred compensation plan assets included in other assets		2,386		—		—			2,386

Total	$	203,362	$	21	$	(268	)	$	203,115

At March 31, 2015 and December 31, 2014, we classified $15.5 million of our aggregate investments as long-term investments and recorded them in our Condensed Consolidated Balance Sheets as Restricted investments, as they are securing outstanding letters of credit with maturities beyond one year.

The following table presents the cost and fair value of our debt investments based on maturities as of:


	March 31, 2015				December 31, 2014
	Amortized		Fair		Amortized		Fair
	Costs		Value		Costs		Value
	(Thousands of dollars)
Due in one year or less	$	95,682	$	95,667	$	70,180	$	70,169
Due within two years		91,336		91,243		62,184		61,948

Total	$	187,018	$	186,910	$	132,364	$	132,117

The following table presents the average coupon rate percentage and the average days to maturity of our debt investments as of:


	March 31, 2015				December 31, 2014
	Average		Average		Average		Average
	Coupon		Days To		Coupon		Days To
	Rate (%)		Maturity		Rate (%)		Maturity
U.S. Government agencies		0.528		44		0.000		0
Municipal bonds and notes		0.869		700		0.528		134
Corporate bonds and notes		1.814		350		1.828		348

The following table presents the fair value and unrealized losses related to our investments that have been in a continuous unrealized loss position for less than twelve months as of March 31,


	2015					2014
			Unrealized					Unrealized
	Fair Value		Losses			Fair Value		Losses
	(Thousands of dollars)
U.S. Government agencies	$	1,999	$	(1	)	$	—	$	—
Corporate bonds and notes		130,231		(136	)		30,332		(30	)

Total	$	132,230	$	(137	)	$	30,332	$	(30	)

The following table presents the fair value and unrealized losses related to our investments that have been in a continuous unrealized loss position for more than twelve months as of March 31,


	2015					2014
			Unrealized					Unrealized
	Fair Value		Losses			Fair Value		Losses
	(Thousands of dollars)
Corporate bonds and notes	$	1,503	$	(1	)	$	—	$	—

Total	$	1,503	$	(1	)	$	—	$	—

From time to time over the periods covered in our financial statements included herein, our investments have experienced net unrealized losses. We consider these declines in market value to be due to market conditions, and we do not plan to sell these investments prior to maturity. For these reasons, we do not consider any of our investments to be other than temporarily impaired at March 31, 2015 or December 31, 2014. We have also determined that we did not have any other-than-temporary impairments relating to credit losses on debt securities for the three months ended March 31, 2015. For additional information regarding our criteria for making these assessments, see Note 2 to the financial statements included in our Annual Report on Form 10-K for the year ended December 31, 2014.