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 gain (loss), 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. We determine cost, gains, and losses using the specific identification method.

Investments consisted of the following as of June 30, 2016:


			Unrealized		Unrealized			Fair
	Cost Basis		Gains		Losses			Value
	(Thousands of dollars)
Investments:
Money market mutual funds	$	17,231	$	—	$	—		$	17,231
Commercial paper		12,408		—		(15	)		12,393
U.S. Government agencies		28,299		13		—			28,312
Corporate bonds and notes		244,196		191		(65	)		244,322

Subtotal		302,134		204		(80	)		302,258
Deferred compensation plan assets included in other assets		2,386		—		—			2,386

Total	$	304,520	$	204	$	(80	)	$	304,644

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


			Unrealized		Unrealized			Fair
	Cost Basis		Gains		Losses			Value
	(Thousands of dollars)
Investments:
Money market mutual funds	$	18,181	$	—	$	—		$	18,181
Commercial paper		5,986		—		(5	)		5,981
U.S. Government agencies		11,499		—		(30	)		11,469
Corporate bonds and notes		265,069		—		(841	)		264,228

Subtotal		300,735		—		(876	)		299,859
Deferred compensation plan assets included in other assets		2,294		—		—			2,294

Total	$	303,029	$	—	$	(876	)	$	302,153

At June 30, 2016 and December 31, 2015, we classified $13.0 million and $15.3 million, respectively, 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:


	June 30, 2016				December 31, 2015
	Amortized		Fair		Amortized		Fair
	Costs		Value		Costs		Value
	(Thousands of dollars)
Due in one year or less	$	164,123	$	164,071	$	152,444	$	152,212
Due within two years		120,780		120,956		130,110		129,466

Total	$	284,903	$	285,027	$	282,554	$	281,678

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


	June 30, 2016				December 31, 2015
	Average		Average		Average		Average
	Coupon		Days To		Coupon		Days To
	Rate (%)		Maturity		Rate (%)		Maturity
Commercial paper		0.932		279		0.553		154
U.S. Government agencies		0.973		559		0.865		599
Corporate bonds and notes		1.633		507		1.757		331

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:


	June 30, 2016					December 31, 2015
			Unrealized					Unrealized
	Fair Value		Losses			Fair Value		Losses
	(Thousands of dollars)
Commercial paper	$	12,394	$	(15	)	$	5,981	$	(5	)
U.S. Government agencies		5,505		(1	)		8,969		(30	)
Corporate bonds and notes		85,084		(33	)		232,347		(793	)

Total	$	102,983	$	(49	)	$	247,297	$	(828	)

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:


	June 30, 2016					December 31, 2015
			Unrealized					Unrealized
	Fair Value		Losses			Fair Value		Losses
	(Thousands of dollars)
Corporate bonds and notes	$	50,203	$	(31	)	$	28,866	$	(48	)

Total	$	50,203	$	(31	)	$	28,866	$	(48	)

From time to time over the periods covered in our financial statements included herein (and as illustrated in the foregoing tables), our investments have experienced net unrealized losses. We consider these declines in market value to be due to customary market fluctuations, 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 June 30, 2016 or December 31, 2015. We have also determined that we did not have any other-than-temporary impairments relating to credit losses on debt securities for the quarter ended June 30, 2016. 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, 2015.