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, 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
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net Income	$ 13,332	$ 11,034	$ 7,367	$ 8,685	$ 12,343	$ 12,188	$ 9,149	$ 7,601	$ 40,418	$ 41,281	$ 44,669
NET INCOME PER SHARE
Weighted average number of common shares outstanding (basic)									14,688,000	14,223,000	13,835,000
Dilutive securities									586,000	502,000	326,000
Weighted Average common and common equivalent shares outstandding (diluted)									15,274,000	14,725,000	14,161,000
EPS - basic	$ 0.89	$ 0.75	$ 0.50	$ 0.60	$ 0.86	$ 0.85	$ 0.65	$ 0.54	$ 2.75	$ 2.90	$ 3.23
EPS - diluted	$ 0.86	$ 0.72	$ 0.48	$ 0.58	$ 0.82	$ 0.82	$ 0.63	$ 0.53	$ 2.65	$ 2.80	$ 3.15
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount									10,000	7,000	217,000