Net Income Per Common Share (Tables)

12 Months Ended

Dec. 31, 2012

Earnings Per Share [Abstract]

Computation of net income per common share

	2012			2011			2010
Basic
Average common shares outstanding	101,714,901			103,471,323			107,021,624
Net income	$	631,034		$	441,860		$	462,485
Less net income allocated to unvested restricted shares	(5,114		)	(4,825		)	(4,817		)
Net income allocated to common shares	$	625,920		$	437,035		$	457,668
Net income per common share	$	6.15		$	4.22		$	4.28
Diluted
Average common shares outstanding	101,714,901			103,471,323			107,021,624
Stock options and other contingently issuable shares (a)	2,215,528			2,200,650			1,763,893
Average common shares outstanding assuming dilution	103,930,429			105,671,973			108,785,517
Net income	$	631,034		$	441,860		$	462,485
Less net income allocated to unvested restricted shares assuming dilution	(5,008		)	(4,756		)	(4,749		)
Net income allocated to common shares assuming dilution	$	626,026		$	437,104		$	457,736
Net income per common share	$	6.02		$	4.14		$	4.21

(a) Stock options and other contingently issuable shares excludes 1,047,734, 101,260 and 1,544,620 shares at December 31, 2012, 2011 and 2010, respectively, due to their anti-dilutive effect.