Earnings per Share (Reconciliation between Basic and Diluted Earnings per Share) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Earnings Per Share [Abstract]
Net income for basic and diluted earnings per share	$ 13,542	$ 18,067	$ 30,886	$ 33,752
Basic weighted average shares outstanding	37,210	36,908	37,189	36,679
Dilutive effect of stock options and restricted stock awards	1,579	1,919	1,595	2,496
Diluted weighted average shares outstanding	38,789	38,827	38,784	39,175
Basic earnings per common share	$ 0.36	$ 0.49	$ 0.83	$ 0.92
Diluted earnings per common share	$ 0.35	$ 0.47	$ 0.80	$ 0.86