Earnings per Share (Details) (USD $) In Thousands, except Per Share data	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Income from continuing operations, net of tax	$ 31,145	$ 20,691	$ 53,267	$ 36,667
Loss from discontinued operations, net of tax	0	(56)	0	(72)
Net income	$ 31,145	$ 20,635	$ 53,267	$ 36,595
Weighted average common shares outstanding - Basic	39,903	38,831	39,695	38,711
Dilutive effect of employee stock grants	636	408	648	381
Weighted average shares - Diluted	42,757	41,723	42,654	41,595
Basic earnings per common share from continuing operations	$ 0.78	$ 0.53	$ 1.34	$ 0.95
Basic loss per common share from discontinued operations	$ 0.00	$ 0.00	$ 0.00	$ 0.00
Basic earnings per common share	$ 0.78	$ 0.53	$ 1.34	$ 0.95
Diluted earnings per common share from continuing operations	$ 0.73	$ 0.50	$ 1.25	$ 0.88
Diluted loss per common share from discontinued operations	$ 0.00	$ 0.00	$ 0.00	$ 0.00
Diluted earnings per common share	$ 0.73	$ 0.49	$ 1.25	$ 0.88
Class B common shares [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Weighted average common shares outstanding - Basic	2,218	2,484	2,311	2,503