Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Earnings Per Share [Abstract]
Distributed earnings allocated to common stock	$ 5,751	$ 5,146	$ 11,502	$ 10,291
Undistributed earnings allocated to common stock	7,139	2,208	9,303	7,011
Net earnings allocated to common shareholders	$ 12,890	$ 7,354	$ 20,805	$ 17,302
Average shares outstanding (in shares)	15,582,000	14,680,000	15,521,000	14,676,000
Effect of dilutive securities:
Warrants outstanding (in shares)	62,000	0	59,000	0
Employee stock options (in shares)	108,000	79,000	107,000	84,000
Shares for diluted earnings per share (in shares)	15,752,000	14,759,000	15,687,000	14,760,000
Basic earnings per share (in dollars per share)	$ 0.83	$ 0.50	$ 1.34	$ 1.18
Diluted earnings per share (in dollars per share)	$ 0.82	$ 0.50	$ 1.33	$ 1.17
Options to purchase shares of common stock, anti-dilutive (in shares)	57,500	208,900
Common stock exercise price, lower limit (in dollars per share)	$ 39.34	$ 32.93
Common stock exercise price, upper limit (in dollars per share)	$ 40.88	$ 40.88