Stock-Based Compensation Plans (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Restricted and performance-based stock, weighted average grant date fair value per share [Roll Forward]
Compensation expense, gross	$ 546,000	$ 443,000
Stock Options [Member]
Options, shares [Roll Forward]
Outstanding, beginning of period (in shares)	29,150
Expired (in shares)	0
Exercised (in shares)	(7,275)
Forfeited, other (in shares)	0
Outstanding, end of period (in shares)	21,875
Options exercisable, end of period (in shares)	21,875
Options, weighted average exercise price [Roll Forward]
Outstanding, beginning of period (in dollars per share)	$ 12.20
Expired (in dollars per share)	$ 0
Exercised (in dollars per share)	$ 12.42
Forfeited, other (in dollars per share)	$ 0
Outstanding, end of period (in dollars per share)	$ 12.13
Options exercisable, end of period (in dollars per share)	$ 12.13
Options, additional disclosures [Abstract]
Outstanding, weighted average remaining contractual term, beginning of period	1 year 10 months 24 days
Outstanding, weighted average remaining contractual term, end of period	1 year 9 months 18 days
Options exercisable, weighted average remaining contractual term, end of period	1 year 9 months 18 days
Aggregate intrinsic value of outstanding stock options	300,000
Total intrinsic value of options exercised	100,000
Options granted (in shares)	0
Performance-based Shares [Member]
Restricted and Performance Stock Grants [Abstract]
Measuring period for performance-based shares	3 years
Award vesting rights	Selected executives and other key personnel are granted performance awards whose vesting is contingent upon meeting various performance measures with a retention feature. Performance-based shares are subject to a three year measuring period and the achievement of performance targets and, depending upon the achievement of such performance targets, they may become vested on the third anniversary of the date of grant.
Restricted and Performance-based Shares [Member]
Restricted and Performance Stock Grants [Abstract]
Award vesting rights	Restricted shares granted to employees become fully vested upon the third anniversary of the date of grant; and for selected key executives certain additional restricted share grants vest 25% upon the attainment of age 60, 25% upon the attainment of age 63 and become fully vested upon the attainment of age 65. Restricted shares granted to directors become fully vested upon the first anniversary of the date of grant.
Restricted and performance-based stock, shares [Roll Forward]
Beginning of period (in shares)	533,625
Granted (in shares)	0
Vested (in shares)	(600)
Forfeited (in shares)	(1,175)
End of period (in shares)	531,850
Restricted and performance-based stock, weighted average grant date fair value per share [Roll Forward]
Beginning of period (in dollars per share)	$ 13.03
Granted (in dollars per share)	$ 0
Vested (in dollars per share)	$ 13.11
Forfeited (in dollars per share)	$ 13.74
End of period (in dollars per share)	$ 13.03
Compensation expense, gross	533,852	430,153
Compensation expense, net of tax	334,621	264,114
Unamortized compensation expense	$ 4,600,000
Restricted and Performance-based Shares [Member] | Employees [Member]
Restricted and Performance Stock Grants [Abstract]
Estimated forfeitures (in hundredths)	5.00%
Restricted and performance-based stock, weighted average grant date fair value per share [Roll Forward]
Weighted average period of recognition for unrecognized compensation expense	5 years 1 month 6 days
Restricted and Performance-based Shares [Member] | Executives [Member]
Restricted and Performance Stock Grants [Abstract]
Estimated forfeitures (in hundredths)	0.00%
Restricted and Performance-based Shares [Member] | Directors [Member]
Restricted and Performance Stock Grants [Abstract]
Estimated forfeitures (in hundredths)	0.00%
Restricted and performance-based stock, weighted average grant date fair value per share [Roll Forward]
Weighted average period of recognition for unrecognized compensation expense	2 months 12 days
Restricted and Performance-based Shares [Member] | Age 60 [Member]
Restricted and Performance Stock Grants [Abstract]
Vesting percentage (in hundredths)	25.00%
Restricted and Performance-based Shares [Member] | Age 63 [Member]
Restricted and Performance Stock Grants [Abstract]
Vesting percentage (in hundredths)	25.00%