Earnings Per Share (Tables)

12 Months Ended

Dec. 31, 2012

Earnings (Loss) Per Share [Abstract]

Earnings Per Share Summary

	Year Ended December 31,
($ thousands, except share and per share data)	2012		2011		2010
Numerator
Net income attributable to common stockholders	$	131,343	$	112,788	$	67,726
Less: income allocated to participating securities		(645)		(1,014)		(863)
Net income attributable to common stockholders - basic and diluted	$	130,698	$	111,774	$	66,863
Denominator
Weighted average common shares outstanding - basic		89,571,105		88,317,898		85,482,055
Plus: dilutive effect of stock options and unvested restricted stock units		1,017,311		1,663,484		2,113,563
Weighted average common shares outstanding - diluted		90,588,416		89,981,382		87,595,618
Net income attributable per common share:
Basic	$	1.46	$	1.27	$	0.78
Diluted	$	1.44	$	1.24	$	0.76