Significant Accounting Policies (Details 3) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Income (Loss) from Continuing Operations, Net of Tax									$ 119,493	$ 78,669	$ 59,929
(Loss)/income from discontinued operations, net of tax	1	(10)	0	0	(82)	2,745	(56)	(16)	(9)	2,591	1,398
Net Income (Loss) Attributable to Parent									$ 119,484	$ 81,260	$ 61,327
Weighted Average Number of Shares Outstanding, Basic									39,912,000	38,886,000	36,146,000
Dilutive Effect of Employee Stock Grants									603,000	475,000	267,000
Weighted average shares - diluted									42,772,000	41,889,000	38,974,000
Basic earnings per common share from continuing operations									$ 2.99	$ 2.02	$ 1.66
Basic earnings per common share from discontinued operations									$ 0.00	$ 0.07	$ 0.04
Basic earnings per common share									$ 2.99	$ 2.09	$ 1.70
Diluted earnings per common share from continuing operations	$ 0.77	$ 0.77	$ 0.73	$ 0.52	$ 0.47	$ 0.53	$ 0.50	$ 0.39	$ 2.79	$ 1.88	$ 1.54
Diluted loss per common share from discontinued operations	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.07	$ 0.00	$ 0.00	$ 0.00	$ 0.06	$ 0.04
Diluted earnings per common share	$ 0.77	$ 0.77	$ 0.73	$ 0.52	$ 0.47	$ 0.59	$ 0.49	$ 0.39	$ 2.79	$ 1.94	$ 1.57
Stock Issued During Period, Shares, New Issues											4,600,000
Stock Issued During Period, Per Share Value, New Issues											$ 24.50
Antidilutive shares									126,000	312,000	1,597,000
Common Class B [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Weighted Average Number of Shares Outstanding, Basic									2,257,000	2,528,000	2,561,000