Net Income Per Common Share (Tables)

9 Months Ended

Sep. 30, 2011

Net Income Per Common Share [Abstract]

Computation of net income per common share

	Three Months Ended						Nine Months Ended
	September 30,						September 30,
(Thousands of dollars except per share data)	2011			2010			2011			2010
Basic
Average common shares outstanding		102,151,164			106,454,042			103,939,552			107,366,658
Net income	$	179,877		$	175,258		$	427,308		$	389,567
Less net income allocated to unvested restricted shares		(2,102	)		(1,930	)		(4,810	)		(4,116	)
Net income allocated to common shares	$	177,775		$	173,328		$	422,498		$	385,451
Basic net income per common share	$	1.74		$	1.63		$	4.06		$	3.59
Diluted
Average common shares outstanding		102,151,164			106,454,042			103,939,552			107,366,658
Stock options and other contingently issuable shares (1)		1,972,108			1,943,695			2,221,992			1,729,278
Average common shares outstanding assuming dilution		104,123,272			108,397,737			106,161,544			109,095,936
Net income	$	179,877		$	175,258		$	427,308		$	389,567
Less net income allocated to unvested restricted shares assuming dilution		(2,070	)		(1,901	)		(4,736	)		(4,055	)
Net income allocated to common shares assuming dilution	$	177,807		$	173,357		$	422,572		$	385,512
Diluted net income per common share	$	1.71		$	1.60		$	3.98		$	3.53

⁽¹⁾ Stock options and other contingently issuable shares excludes 0.1 million shares for the nine months ended September 30, 2011 and September 30, 2010 due to their anti-dilutive effect. There were 0.1 million shares excluded due to their anti-dilutive effect for the three months ended September 30, 2011 and none for the three months ended September 30, 2010.