Earnings per Share (Details) (USD $) Share data in Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended				6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011 3.50% Senior Convertible Notes due 2027	Dec. 31, 2010 3.50% Senior Convertible Notes due 2027	Jun. 30, 2011 Performance Share Awards Under the Equity Incentive Compensation Plan
Earnings per share
Performance period to receive awards (in years)							three years
Common stock awards vesting multiplier, low end of range							0
Common stock awards vesting multiplier, high end of range							2
Interest rate on notes (as a percent)					3.50%	3.50%
Principal amount surrendered for debt instrument conversion					$ 1,000
Common stock conversion price (in dollars per share)					$ 54.42
Calculation of basic and diluted earnings per share
Net income (in dollars)	$ 124,533,000	$ 18,068,000	$ 106,030,000	$ 144,246,000
Basic weighted-average common shares outstanding (in shares)	63,638	62,917	63,543	62,855
Add: dilutive effect of stock options, unvested RSUs, and contingent PSAs (in shares)	2,182	1,649	2,161	1,638
Add: dilutive effect of 3.50% Senior Convertible Notes (in shares)	1,089		991
Diluted weighted-average common shares outstanding (in shares)	66,909	64,566	66,695	64,493
Basic net income per common share (in dollars per share)	$ 1.96	$ 0.29	$ 1.67	$ 2.29
Diluted net income per common share (in dollars per share)	$ 1.86	$ 0.28	$ 1.59	$ 2.24