Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Summary of earnings per share
NET INCOME	$ 11,601	$ 11,959	$ 32,658	$ 34,267
Weighted Average Shares (in shares)
BASIC SHARES	21,654,188	21,463,714	21,613,157	21,401,885
EFFECT OF DILUTIVE SECURITIES	52,116	13,077	31,300	32,452
DILUTIVE SHARES	21,706,304	21,476,791	21,644,457	21,434,337
NET INCOME PER SHARE (in dollars per share)
BASIC EPS	$ 0.54	$ 0.56	$ 1.51	$ 1.60
EFFECT OF DILUTIVE SECURITIES	$ 0.01
DILUTIVE EPS	$ 0.53	$ 0.56	$ 1.51	$ 1.60