Summary of Significant Accounting Policies Net Income Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net Income	$ 12,343	$ 12,188	$ 9,149	$ 7,601	$ 17,842	$ 9,261	$ 9,493	$ 8,073	$ 41,281	$ 44,669	$ 29,923
NET INCOME PER SHARE
Weighted average number of common shares outstanding (basic)									14,223,000	13,835,000	13,611,000
Dilutive securities									502,000	326,000	244,000
Weighted Average common and common equivalent shares outstandding (diluted)									14,725,000	14,161,000	13,855,000
EPS - basic	$ 0.86	$ 0.85	$ 0.65	$ 0.54	$ 1.29	$ 0.66	$ 0.69	$ 0.59	$ 2.90	$ 3.23	$ 2.20
EPS - diluted	$ 0.82	$ 0.82	$ 0.63	$ 0.53	$ 1.26	$ 0.65	$ 0.67	$ 0.57	$ 2.80	$ 3.15	$ 2.16
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount									7,000	217,000	524,000