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, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount									217,000	524,000	407,000
NET INCOME PER SHARE
Net income	$ 17,842	$ 9,261	$ 9,493	$ 8,073	$ 9,681	$ 8,817	$ 7,566	$ 3,859	$ 44,669	$ 29,923	$ 24,981
Weighted average number of common shares outstanding (basic)									13,835,000	13,611,000	14,720,000
Dilutive securities									326,000	244,000	264,000
Weighted Average common and common equivalent shares outstandding (diluted)									14,161,000	13,855,000	14,984,000
EPS - basic	$ 1.29	$ 0.66	$ 0.69	$ 0.59	$ 0.71	$ 0.65	$ 0.56	$ 0.28	$ 3.23	$ 2.20	$ 1.70
EPS - diluted	$ 1.26	$ 0.65	$ 0.67	$ 0.57	$ 0.70	$ 0.64	$ 0.55	$ 0.27	$ 3.15	$ 2.16	$ 1.67