Earnings Per Share (Tables)

12 Months Ended

Dec. 31, 2014

Earnings Per Share [Abstract]

Computation of Earnings Per Common Share

A summary of the information used in the computation of earnings per common share follows:

	Years Ended December 31,
($ in thousands, except per share amounts)	2014		2013		2012
Numerator:
Net income to common shareholders	$	175,722	$	163,356	$	151,742
Net income allocated to participating securities - basic and diluted		3,631		3,105		1,557
Net income allocated to common shareholders - basic and diluted	$	172,091	$	160,251	$	150,185
Denominator:
Weighted-average common shares - basic		81,804		83,066		84,767
Dilutive potential common shares		230		101		821
Weighted average common shares - diluted		82,034		83,167		85,588
Earnings per common share:
Basic	$	2.10	$	1.93	$	1.77
Diluted	$	2.10	$	1.93	$	1.75