Investments (Tables)

12 Months Ended

Dec. 31, 2014

Investments, Debt and Equity Securities [Abstract]

Components of Investments

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

Investments consisted of the following as of December 31, 2013:

			Unrealized		Unrealized			Fair
	Cost Basis		Gains		Losses			Value
	(Thousands of dollars)
Investments:
Money Market Mutual Funds	$	18,470	$	—	$	—		$	18,470
Commercial Paper		2,999		—		—			2,999
Municipal bonds and notes		1,500		—		(1	)		1,499
Corporate bonds and notes		77,595		67		(29	)		77,633
Subtotal		100,564		67		(30	)		100,601
Deferred compensation plan assets included in other assets		2,109		—		—			2,109
Total	$	102,673	$	67	$	(30	)	$	102,710

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 December 31,

	2014				2013
	Amortized		Fair		Amortized		Fair
	Costs		Value		Costs		Value
	(Thousands of dollars)
Due in one year or less	$	70,180	$	70,169	$	32,536	$	32,538
Due within two years		62,184		61,948		49,558		49,593
Total	$	132,364	$	132,117	$	82,094	$	82,131

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 December 31,

	2014				2013
	Average Coupon Rate (%)		Average Days To Maturity		Average Coupon Rate (%)		Average Days To Maturity
Commercial Paper		0.000		0		0.150		86
Municipal bonds and notes		0.528		134		0.528		499
Corporate bonds and notes		1.828		348		2.134		390

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 December 31,

	2014					2013
			Unrealized					Unrealized
	Fair Value		Losses			Fair Value		Losses
	(Thousands of dollars)
Commercial Paper	$	—	$	—		$	—	$	—
Municipal bonds and notes		—		—			1,499		(1	)
Corporate bonds and notes		100,071		(268	)		34,772		(29	)
Total	$	100,071	$	(268	)	$	36,271	$	(30	)