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 March 31, 2017:


			Unrealized		Unrealized			Fair
	Cost Basis		Gains		Losses			Value
	(Thousands of dollars)
Investments:
Money market mutual funds	$	10,597	$	—	$	—		$	10,597
Commercial paper		27,935		—		(26	)		27,909
U.S. Government agencies		15,305		—		(20	)		15,285
Corporate bonds and notes		236,525		4		(479	)		236,050

Subtotal		290,362		4		(525	)		289,841
Deferred compensation plan assets included in other assets		2,500		—		—			2,500

Total	$	292,862	$	4	$	(525	)	$	292,341

Investments consisted of the following as of December 31, 2016:


			Unrealized		Unrealized			Fair
	Cost Basis		Gains		Losses			Value
	(Thousands of dollars)
Investments:
Money market mutual funds	$	18,118	$	—	$	—		$	18,118
Commercial paper		27,906		—		(39	)		27,867
U.S. government agencies		13,295		—		(32	)		13,263
Corporate bonds and notes		244,202		2		(622	)		243,582

Subtotal		303,521		2		(693	)		302,830
Deferred compensation plan assets included in other assets		2,394		—		—			2,394

Total	$	305,915	$	2	$	(693	)	$	305,224

At March 31, 2017 and December 31, 2016, we classified $13.0 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 and a bond relating to foreign operations.

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


	March 31, 2017				December 31, 2016
	Amortized		Fair		Amortized		Fair
	Costs		Value		Costs		Value
	(Thousands of dollars)
Due in one year or less	$	200,195	$	199,906	$	184,587	$	184,334
Due within two years		79,570		79,338		100,816		100,378

Total	$	279,765	$	279,244	$	285,403	$	284,712

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


	March 31, 2017				December 31, 2016
	Average		Average		Average		Average
	Coupon		Days To		Coupon		Days To
	Rate (%)		Maturity		Rate (%)		Maturity
Commercial paper		1.035		140		1.001		184
U.S. Government agencies		1.056		355		0.970		400
Corporate bonds and notes		1.731		287		1.745		318

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, 2017					December 31, 2016
			Unrealized					Unrealized
	Fair Value		Losses			Fair Value		Losses
	(Thousands of dollars)
Commercial paper	$	27,909	$	(26	)	$	27,867	$	(39	)
U.S. Government agencies		14,285		(20	)		13,263		(32	)
Corporate bonds and notes		207,512		(460	)		210,836		(602	)

Total	$	249,706	$	(506	)	$	251,966	$	(673	)

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, 2017					December 31, 2016
			Unrealized					Unrealized
	Fair Value		Losses			Fair Value		Losses
	(Thousands of dollars)
Corporate bonds and notes	$	20,116	$	(19	)	$	24,196	$	(20	)

Total	$	20,116	$	(19	)	$	24,196	$	(20	)

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 March 31, 2017 or December 31, 2016. 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 March 31, 2017. 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, 2016.