Summary Of Significant Accounting Policies (Schedule Of Calculation Of Basic And Diluted Earnings Per Share) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended												12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Summary Of Significant Accounting Policies [Abstract]
Net income	$ 18,115	$ 19,314	$ 13,580	$ 5,598	$ 2,878	$ 19,867	$ 14,701	$ 14,513	$ 19,010	$ 22,469	$ 20,137	$ 18,142	$ 56,607	$ 51,959	$ 79,758
Denominator for basic earnings per share - weighted-average number of common shares outstanding during the period													56,320	59,284	62,141
Incremental common shares attributable to exercise of outstanding dilutive options													150	270	455
Incremental common shares attributable to outstanding restricted shares, restricted stock units and phantom stock													164	219	96
Denominator for diluted earnings per share													56,634	59,773	62,692
Basic earnings per share	$ 0.33	$ 0.35	$ 0.24	$ 0.10	$ 0.05	$ 0.34	$ 0.24	$ 0.24	$ 0.31	$ 0.36	$ 0.32	$ 0.29	$ 1.01	$ 0.88	$ 1.28
Diluted earnings per share	$ 0.33	$ 0.34	$ 0.24	$ 0.10	$ 0.05	$ 0.34	$ 0.24	$ 0.24	$ 0.31	$ 0.36	$ 0.32	$ 0.28	$ 1.00	$ 0.87	$ 1.27