Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Numerator:
Net Earnings	$ 10,301	$ 10,617	$ 14,254	$ 5,059	$ 13,844	$ 8,745	$ 13,671	$ 5,324	$ 40,231	$ 41,584	$ 32,713
Basic - Weighted Average Shares Outstanding									18,297,371	18,544,896	18,832,693
Effect of dilutive securities: Employee stock options									536,082	557,120	527,735
Diluted - Weighted Average Shares Outstanding									18,833,453	19,102,016	19,360,428
Basic Earnings per Share	$ 0.56	$ 0.58	$ 0.78	$ 0.28	$ 0.75	$ 0.47	$ 0.74	$ 0.28	$ 2.20	$ 2.24	$ 1.74
Diluted Earnings per Share	$ 0.55	$ 0.56	$ 0.76	$ 0.27	$ 0.73	$ 0.46	$ 0.71	$ 0.28	$ 2.14	$ 2.18	$ 1.69
Anti-dilutive securities excluded from earnings per share calculation (in shares)									132,803	233,655	123,292