Earnings per Share (Details) (USD $) Share data in Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2012 Performance Share Awards Under the Equity Incentive Compensation Plan	Mar. 31, 2012 Convertible Debt [Member]	Dec. 31, 2011 Convertible Debt [Member]
Earnings per share
Performance period to receive awards (in years)	3 years		3
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%
Debt Instrument, Principal Amount Denominator for Conversion into Common Stock				$ 1,000
Common stock conversion price (in dollars per share)				$ 54.42
Calculation of basic and diluted earnings per share
Net income (in dollars)	$ 26,336,000	$ (18,503,000)
Basic weighted-average common shares outstanding (in shares)	64,104	63,447
Add: dilutive effect of stock options, unvested RSUs, and contingent PSAs (in shares)	2,210	0
Add: dilutive effect of 3.50% Senior Convertible Notes (in shares)	1,531	0
Diluted weighted-average common shares outstanding (in shares)	67,845	63,447
Basic net income per common share (in dollars per share)	$ 0.41	$ (0.29)
Diluted net income per common share (in dollars per share)	$ 0.39	$ (0.29)