Weighted Average Shares Outstanding (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Weighted Average Shares Outstanding [Line Items]
Basic (in shares)	55,214,586	55,259,732	53,879,976
Dilutive effect of:
Diluted (in shares)	55,931,882	55,925,187	54,206,426
Trading Days Used To Compute Average Closing Price of Stock for Dilutive Effect Comparison	30 days
Incremental Common Shares Attributable to Conversion of Debt Securities	0	0
3.75% Convertible Notes [Member] | Convertible Debt [Member]
Dilutive effect of:
Convertible notes		92,500
Convertible notes stated interest rate	3.75%
3.375% Convertible Notes [Member] | Convertible Debt [Member]
Dilutive effect of:
Convertible notes stated interest rate	3.375%
Debt Instrument, Convertible, Conversion Price	28.31
Stock options [Member]
Dilutive effect of:
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	787,809	1,730,632	3,560,600
Stock options [Member]
Dilutive effect of:
Shares attributable to share-based payment arrangements (in shares)	645,280	591,943	245,784
Restricted stock units [Member]
Dilutive effect of:
Shares attributable to share-based payment arrangements (in shares)	19,089	4,608	4,318
Non Employee Director Deferred Stock Plan [Member]
Dilutive effect of:
Shares attributable to share-based payment arrangements (in shares)	52,927	68,904	76,348