Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Earnings Per Share [Abstract]
Net earnings	$ 17,533	$ 41,876	$ 46,390	$ 88,009
Basic weighted average shares	52,824,000	54,885,000	52,809,000	56,416,000
Effect of dilutive stock options	250,000	368,000	238,000	378,000
Diluted weighted average shares	53,074,000	55,253,000	53,047,000	56,794,000
Basic earnings per common share	$ 0.33	$ 0.76	$ 0.88	$ 1.56
Diluted earnings per common share	$ 0.33	$ 0.76	$ 0.87	$ 1.55
Earnings Per Share (Details) [Abstract]
Number of anti-dilutive stock awards	2,398,269	1,119,530	2,418,436	1,268,665