Stock Option Plans (Tables)

12 Months Ended

Dec. 31, 2011

Summary of stock-based compensation expense

The following table is a summary of the stock-based compensation expense recognized for the years ended December 31, 2011, 2010 and 2009:

(Thousands of dollars)	2011			2010			2009

Stock-based compensation expense	$	5,310		$	4,627		$	2,943
Tax benefit		(1,964	)		(1,712	)		(1,089	)

Stock-based compensation expense, net of tax	$	3,346		$	2,915		$	1,854

Stock option valuation assumptions

The fair value of each option grant during the years ended December 31, 2011, 2010 and 2009 was estimated on the date of grant using the Black-Scholes option-pricing model with the following assumptions:

	2011			2010			2009

Expected dividend yield		0.60% - .80	%		0.94% - 1.60	%		0.87% - 1.40	%
Expected stock price volatility		48.10% - 57.90	%		51.20% - 57.80	%		23.40% - 28.15	%
Risk free interest rate		0.28% - 2.39	%		0.53% - 2.96	%		0.55% - 1.37	%
Expected life of options	3 - 4 years			2 - 6 years			3 - 7 years
Weighted-average fair value per share at grant date	$	26.29		$	17.05		$	10.13

Summary of stock options activity

A summary of stock option activity under the plans during the year ended December 31, 2011, is presented below:

					Weighted-
				Weighted-	Average		Aggregate
				Average	Remaining		Intrinsic
				Exercise	Contractual		Value
Options	Shares			Price	Term		($000's)
Outstanding at January 1, 2011	1,321,637		$	33.26
Granted	434,948			62.69
Exercised	(188,649	)		27.37
Forfeited or expired	(63,625	)		39.36
Outstanding at December 31, 2011	1,504,311		$	42.26		7.9	$	38,733
Exercisable at December 31, 2011	666,613		$	34.53		6.8	$	22,419