Weighted Average Shares Outstanding (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended						12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Apr. 05, 2011 3.75% Convertible Notes [Member] Convertible Debt [Member]	Dec. 31, 2012 3.375% Convertible Notes [Member] Convertible Debt [Member]	Dec. 31, 2011 3.375% Convertible Notes [Member] Convertible Debt [Member]	Dec. 31, 2012 Stock options [Member]	Dec. 31, 2011 Stock options [Member]	Dec. 31, 2010 Stock options [Member]	Dec. 31, 2012 Stock options [Member]	Dec. 31, 2011 Stock options [Member]	Dec. 31, 2010 Stock options [Member]	Dec. 31, 2012 Restricted stock units [Member]	Dec. 31, 2011 Restricted stock units [Member]	Dec. 31, 2010 Restricted stock units [Member]	Dec. 31, 2012 Non Employee Director Deferred Stock Plan [Member]	Dec. 31, 2011 Non Employee Director Deferred Stock Plan [Member]	Dec. 31, 2010 Non Employee Director Deferred Stock Plan [Member]
Weighted Average Shares Outstanding [Line Items]
Basic (in shares)	54,626,453	55,214,586	55,259,732
Dilutive effect of:
Shares attributable to share-based payment arrangements (in shares)										478,462	645,280	591,943	70,554	19,089	4,608	48,988	52,927	68,904
Diluted (in shares)	55,224,457	55,931,882	55,925,187
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount							336,892	787,809	1,730,632
Convertible notes				$ 92,500	$ 55,636	$ 55,636
Convertible notes stated interest rate				3.75%	3.375%
Debt Instrument, Convertible, Conversion Price					$ 28.31
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	0