Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Numerator:
Net Earnings	$ 17,541	$ 11,792	$ 15,523	$ 5,795	$ 10,301	$ 10,617	$ 14,254	$ 5,059	$ 50,651	$ 40,231	$ 41,584
Basic - Weighted Average Shares Outstanding									18,217,384	18,297,371	18,544,896
Effect of dilutive securities: Employee stock options									523,474	536,082	557,120
Diluted - Weighted Average Shares Outstanding									18,740,858	18,833,453	19,102,016
Basic Earnings per Share	$ 0.96	$ 0.65	$ 0.85	$ 0.32	$ 0.56	$ 0.58	$ 0.78	$ 0.28	$ 2.78	$ 2.20	$ 2.24
Diluted Earnings per Share	$ 0.93	$ 0.63	$ 0.83	$ 0.31	$ 0.55	$ 0.56	$ 0.76	$ 0.27	$ 2.70	$ 2.14	$ 2.18
Anti-dilutive securities excluded from earnings per share calculation (in shares)									91,199	132,803	233,655