Net Income Per Common Share (Tables)

12 Months Ended

Dec. 31, 2014

Earnings Per Share [Abstract]

Computation of net income per common share

	2014			2013			2012
Basic
Average common shares outstanding	96,190,101			100,897,512			101,714,901
Net income	$	865,887		$	752,561		$	631,034
Less net income allocated to unvested restricted shares	(4,892		)	(4,596		)	(5,114		)
Net income allocated to common shares	$	860,995		$	747,965		$	625,920
Net income per common share	$	8.95		$	7.41		$	6.15
Diluted
Average common shares outstanding	96,190,101			100,897,512			101,714,901
Stock options and other contingently issuable shares (a)	1,885,334			2,151,359			2,215,528
Average common shares outstanding assuming dilution	98,075,435			103,048,871			103,930,429
Net income	$	865,887		$	752,561		$	631,034
Less net income allocated to unvested restricted shares assuming dilution	(4,804		)	(4,509		)	(5,008		)
Net income allocated to common shares assuming dilution	$	861,083		$	748,052		$	626,026
Net income per common share	$	8.78		$	7.26		$	6.02

(a) Stock options and other contingently issuable shares excludes 608,477, 842,354 and 1,047,734 shares at December 31, 2014, 2013 and 2012, respectively, due to their anti-dilutive effect.