Earnings Per Share (Tables)

12 Months Ended

Dec. 31, 2018

Earnings Per Share [Abstract]

Computation of Earnings Per Common Share

	Years Ended December 31,
($ in thousands, except per share data)	2018		2017		2016
Numerator:
Net income to common shareholders	$	323,770	$	215,632	$	149,296
Net income allocated to participating securities -- basic and diluted		5,930		4,670		3,598
Net income allocated to common shareholders - basic and diluted	$	317,840	$	210,962	$	145,698
Denominator:
Weighted-average common shares - basic		85,355		84,695		77,850
Dilutive potential common shares		166		268		99
Weighted average common shares - diluted		85,521		84,963		77,949
Earnings per common share:
Basic	$	3.72	$	2.49	$	1.87
Diluted	$	3.72	$	2.48	$	1.87