Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Numerator:
Net Earnings	$ 14,254	$ 13,671	$ 19,313	$ 18,995
Denominator:
Basic - Average Shares Outstanding (in shares)	18,253,326	18,594,207	18,298,379	18,658,182
Effect of dilutive securities - share-based compensation plans	534,554	609,356	537,163	604,287
Diluted - Weighted Average Shares Outstanding (in shares)	18,787,880	19,203,563	18,835,542	19,262,469
Basic Earnings per Share (in dollars per share)	$ 0.78	$ 0.74	$ 1.06	$ 1.02
Diluted Earnings per Share (in dollars per share)	$ 0.76	$ 0.71	$ 1.03	$ 0.99
Anti-dilutive securities excluded from earnings per share calculation (in shares)	278,862	253,781	270,433	208,578