Share-Based Compensation Plans (Details 2) (Restricted Stock Performance Units [Member], USD $)	9 Months Ended
	Sep. 30, 2012
Restricted Stock Performance Units [Member]
Summary of activity for restricted stock performance units
Outstanding at January 1, 2012, Number of shares	130,512
Outstanding at January 1, 2012, Weighted average grant date fair value	$ 20.90
Granted, Number of shares	69,772
Granted, Weighted Average grant date fair value	$ 22.20
Converted into shares of common stock, Number of shares	(35,101)
Converted into shares of common stock, Weighted average grant date fair value	$ 23.28
Forfeited/expired, Number of shares	(8,428)
Forfeited/expired, Weighted average grant date fair value	$ 23.05
Outstanding at June 30, 2012, Number of shares	156,755
Outstanding at June 30, 2012, Weighted average grant date fair value	$ 20.83