Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Earnings Per Share Reconciliation [Abstract]
Net earnings	$ 28,539	$ 30,935
Net earnings available to participating securities	(436)	0
Net earnings available to common shareholders	$ 28,103	$ 30,935
Weighted-average outstanding shares of common stock - basic	46,400,441	45,093,127
Dilutive effect of equity incentive plans	394,162	1,465,416
Weighted-average outstanding shares of common stock - diluted	46,794,603	46,558,543
Basic	$ 0.61	$ 0.69
Diluted	$ 0.60	$ 0.66
Share options excluded from the computation of diluted earnings per share	430,319	302,000