Stock-Based Compensation Plans (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Restricted and performance-based stock, weighted average grant date fair value per share [Roll Forward]
Compensation expense, gross	$ 3,948	$ 2,940
Stock Options [Member]
Options, shares [Roll Forward]
Outstanding, beginning of period (in shares)	9,875
Expired (in shares)	0
Exercised (in shares)	(9,875)
Forfeited, other (in shares)	0
Outstanding, end of period (in shares)	0		9,875
Options exercisable, end of period (in shares)	0
Options, weighted average exercise price [Roll Forward]
Outstanding, beginning of period (in dollars per share)	$ 10.99
Expired (in dollars per share)	0
Exercised (in dollars per share)	10.99
Forfeited, other (in dollars per share)	0
Outstanding, end of period (in dollars per share)	0		$ 10.99
Options exercisable, end of period (in dollars per share)	$ 0
Options, additional disclosures [Abstract]
Outstanding, weighted average remaining contractual term	0 years		4 months 24 days
Options exercisable, weighted average remaining contractual term, end of period	0 years
Total intrinsic value of options exercised	$ 300
Options granted (in shares)	0
Performance-based Shares [Member]
Restricted and Performance Stock Grants [Abstract]
Measuring period for performance-based shares	3 years
Restricted Shares [Member] | Employees [Member]
Restricted and Performance Stock Grants [Abstract]
Estimated forfeitures	5.00%
Restricted Shares [Member] | Executives [Member]
Restricted and Performance Stock Grants [Abstract]
Estimated forfeitures	0.00%
Restricted Shares [Member] | Directors [Member]
Restricted and Performance Stock Grants [Abstract]
Estimated forfeitures	0.00%
Restricted Shares [Member] | Age 60 [Member]
Restricted and Performance Stock Grants [Abstract]
Vesting percentage	25.00%
Restricted Shares [Member] | Age 63 [Member]
Restricted and Performance Stock Grants [Abstract]
Vesting percentage	25.00%
Restricted Shares [Member] | Age65 [Member]
Restricted and Performance Stock Grants [Abstract]
Vesting percentage	100.00%
Restricted and Performance-based Shares [Member]
Restricted and performance-based stock, shares [Roll Forward]
Beginning of period (in shares)	749,018
Granted (in shares)	7,000
Vested (in shares)	(48,918)
Forfeited (in shares)	(4,250)
End of period (in shares)	702,850		749,018
Restricted and performance-based stock, weighted average grant date fair value per share [Roll Forward]
Beginning of period (in dollars per share)	$ 24.62
Granted (in dollars per share)	35.07
Vested (in dollars per share)	33.07
Forfeited (in dollars per share)	25.70
End of period (in dollars per share)	$ 24.13		$ 24.62
Compensation expense, gross	$ 3,600	2,500
Compensation expense, net of tax	2,300	$ 1,600
Unamortized compensation expense	$ 8,200
Restricted and Performance-based Shares [Member] | Employees [Member]
Restricted and performance-based stock, weighted average grant date fair value per share [Roll Forward]
Weighted average period of recognition for unrecognized compensation expense	4 years 6 months
Restricted and Performance-based Shares [Member] | Directors [Member]
Restricted and performance-based stock, weighted average grant date fair value per share [Roll Forward]
Weighted average period of recognition for unrecognized compensation expense	7 months 6 days