Earnings per Share (Details) (USD $) In Thousands, except Per Share data	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Income from continuing operations, net of tax	$ 32,952	$ 22,050	$ 86,219	$ 58,717
(Loss)/income from discontinued operations, net of tax	(10)	2,745	(10)	2,673
Net income	$ 32,942	$ 24,795	$ 86,209	$ 61,390
Weighted average common shares outstanding - Basic	40,078	38,940	39,825	38,774
Dilutive effect of employee stock grants	537	491	610	412
Weighted average shares - Diluted	42,821	41,894	42,711	41,675
Basic earnings per common share from continuing operations	$ 0.82	$ 0.57	$ 2.16	$ 1.51
Basic (loss)/income per common share from discontinued operations	$ 0.00	$ 0.07	$ 0.00	$ 0.07
Basic earnings per common share	$ 0.82	$ 0.64	$ 2.16	$ 1.58
Diluted earnings per common share from continuing operations	$ 0.77	$ 0.53	$ 2.02	$ 1.41
Diluted (loss)/income per common share from discontinued operations	$ 0.00	$ 0.07	$ 0.00	$ 0.06
Diluted earnings per common share	$ 0.77	$ 0.59	$ 2.02	$ 1.47
Class B common shares [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Weighted average common shares outstanding - Basic	2,206	2,463	2,276	2,489