Earnings Per Share (Schedule Computing Earnings Per Share) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Earnings Per Share [Abstract]
Net income available to common shareholders	$ 9,463	$ 16,674	$ 22,759	$ 42,169
Weighted average number of shares used in calculating basic net income per share	31,363	31,278	31,340	31,255
Stock options	35	75	58	112
Long-term incentive plan	152	109	152	109
Weighted average number of shares used in calculating diluted net income per share	31,550	31,462	31,550	31,476
Effect of stock-based compensation plans that were not included in the computation of diluted earnings per share because to do so would have been antidilutive
Average market price of common stock used for calculation of dilutive shares	$ 19.92	$ 22.24	$ 21.46	$ 23.78
Basic	$ 0.3	$ 0.53	$ 0.73	$ 1.35
Diluted	$ 0.3	$ 0.53	$ 0.72	$ 1.34