Net Income Per Common Share (Tables)

6 Months Ended

Jun. 30, 2011

Net Income Per Common Share [Abstract]

Computation of net income per common share

	Three Months Ended						Six Months Ended
	June 30,						June 30,
(Thousands of dollars except per share data)	2011			2010			2011			2010
Basic
Average common shares outstanding		104,676,477			107,686,335			104,833,745			107,822,967
Net income	$	179,115		$	181,706		$	247,431		$	214,309
Less net income allocated to unvested restricted shares		(2,039	)		(1,983	)		(2,709	)		(2,186	)
Net income allocated to common shares	$	177,076		$	179,723		$	244,722		$	212,123
Basic net income per common share	$	1.69		$	1.67		$	2.33		$	1.97
Diluted
Average common shares outstanding		104,676,477			107,686,335			104,833,745			107,822,967
Stock options and other contingently issuable shares (1)		2,199,984			2,146,317			2,270,280			1,637,652
Average common shares outstanding assuming dilution		106,876,461			109,832,652			107,104,025			109,460,619
Net income	$	179,115		$	181,706		$	247,431		$	214,309
Less net income allocated to unvested restricted shares assuming dilution		(2,004	)		(1,950	)		(2,666	)		(2,154	)
Net income allocated to common shares assuming dilution	$	177,111		$	179,756		$	244,765		$	212,155
Diluted net income per common share	$	1.66		$	1.64		$	2.29		$	1.94

⁽¹⁾ Stock options and other contingently issuable shares excludes 0.1 million shares for the six months ended June 30, 2011 and June 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 June 30, 2011 and none for the three months ended June 30, 2010.