Earnings Per Share Computation of diluted weighted average shares outstanding (Details)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	3,679,000	1,956,000	4,973,000
Weighted average shares outstanding - basic	50,529,476	50,944,349	50,857,812
Weighted average number diluted shares outstanding adjustment	883,034	785,164
Weighted average shares outstanding - diluted	51,412,510	51,729,513	50,857,812
3.5% Issue [Member]
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Debt Instrument, convertible, number of equity instruments	88,587