Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Earnings Per Share [Abstract]
Distributed earnings allocated to common stock	$ 5,767	$ 5,150	$ 17,302	$ 15,451
Undistributed earnings allocated to common stock	8,081	5,373	17,349	12,375
Net earnings allocated to common shareholders	$ 13,848	$ 10,523	$ 34,651	$ 27,826
Average shares outstanding (in shares)	15,608,000	14,751,000	15,545,000	14,700,000
Effect of dilutive securities:
Warrants outstanding (in shares)	62,000	0	60,000	0
Employee stock awards (in shares)	120,000	83,000	108,000	83,000
Shares for diluted earnings per share (in shares)	15,790,000	14,834,000	15,713,000	14,783,000
Basic earnings per share (in dollars per share)	$ 0.89	$ 0.71	$ 2.23	$ 1.89
Diluted earnings per share (in dollars per share)	$ 0.88	$ 0.71	$ 2.21	$ 1.88
Options to purchase shares of common stock, anti-dilutive (in shares)	0	124,000
Common stock exercise price, lower limit (in dollars per share)		$ 35.09
Common stock exercise price, upper limit (in dollars per share)		$ 40.88