Investments (Tables)

3 Months Ended

Mar. 31, 2016

Investments, Debt and Equity Securities [Abstract]

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


	Cost Basis		Unrealized Gains		Unrealized Losses			Fair Value
	(Thousands of dollars)
Investments:
Money market mutual funds	$	17,877	$	—	$	—		$	17,877
Commercial paper		5,994		1		—			5,995
U.S. Government agencies		27,301		7		(6	)		27,302
Corporate bonds and notes		250,399		94		(192	)		250,301

Subtotal		301,571		102		(198	)		301,475
Deferred compensation plan assets included in other assets		2,334		—		—			2,334

Total	$	303,905	$	102	$	(198	)	$	303,809

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


	Cost Basis		Unrealized Gains		Unrealized Losses			Fair 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

Cost and Fair Value of Debt Investments Based on Maturities

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


	March 31, 2016				December 31, 2015
	Amortized Costs		Fair Value		Amortized Costs		Fair Value
	(Thousands of dollars)
Due in one year or less	$	148,590	$	148,516	$	152,444	$	152,212
Due within two years		135,104		135,082		130,110		129,466

Total	$	283,694	$	283,598	$	282,554	$	281,678

Average Coupon Rate Percentage and Average Days to Maturity of Debt

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


	March 31, 2016				December 31, 2015
	Average Coupon Rate (%)		Average Days To Maturity		Average Coupon Rate (%)		Average Days To Maturity
Commercial paper		0.553		63		0.553		154
U.S. Government agencies		0.985		602		0.865		599
Corporate bonds and notes		1.727		328		1.757		331

Investments in Continuous Unrealized Loss Position for Less Than Twelve Months

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, 2016					December 31, 2015
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
	(Thousands of dollars)
Commercial paper	$	0	$	0		$	5,981	$	(5	)
U.S. Government agencies		11,996		(6	)		8,969		(30	)
Corporate bonds and notes		134,298		(150	)		232,347		(793	)

Total	$	146,294	$	(156	)	$	247,297	$	(828	)

Investments in Continuous Unrealized Loss Position for More Than Twelve Months

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, 2016					December 31, 2015
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
	(Thousands of dollars)
Corporate bonds and notes	$	47,783	$	(42	)	$	28,866	$	(48	)

Total	$	47,783	$	(42	)	$	28,866	$	(48	)

- Definition

Tabular disclosure of available-for-sale securities which includes, but is not limited to, changes in the cost basis and fair value, fair value and gross unrealized gain (loss), fair values by type of security, contractual maturity and classification, amortized cost basis, contracts to acquire securities to be accounted for as available-for-sale, debt maturities, transfers to trading, change in net unrealized holding gain (loss) net of tax, continuous unrealized loss position fair value, aggregate losses qualitative disclosures, other than temporary impairment (OTTI) losses or other disclosures related to available for sale securities.

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