Earnings Per Common Share (Details) (USD $) In Thousands, except Share data	3 Months Ended				6 Months Ended				12 Months Ended
	Jun. 30, 2011		Jun. 30, 2010		Jun. 30, 2011		Jun. 30, 2010		Dec. 31, 2010
Earnings Per Share [Abstract]
Net Income	$ 56,454		$ 38,558		$ 114,865		$ 95,511		$ 217,586
Shares used for determining basic earnings per share	81,128,442		80,104,004		81,038,096		79,923,790
Dilutive Effect of:
Stock Options	494,374		374,768		487,376		387,399
Performance and restricted shares	634,627		613,931		611,325		592,281
Assumed conversion of Senior Exchangeable Notes	1,541,395	[1]	0	[1]	1,271,207	[1]	0	[1]
Assumed conversion of warrants	328,778	[1]	0	[1]	104,321	[1]	0	[1]
Shares used for determining diluted earnings per common share	84,127,616		81,092,703		83,512,325		80,903,470
Basic earnings per common share	$ 0.70		$ 0.48		$ 1.42		$ 1.20
Diluted earnings per common share	$ 0.67		$ 0.48		$ 1.38		$ 1.18

[1] (a) For additional information on the potential dilutive impact of the Senior Exchangeable Notes, warrants and exchangeable note hedges, see Note 11 - Debt in the 2010 Annual Report on Form 10-K.