Share Based Compensation (Details 2) (USD $)	9 Months Ended
	Sep. 30, 2012
Restricted Stock RSU [Member]
Summary of liability-based award activity
Balance at January 1, 2012	$ 19.07
Balance at January 1, 2012, Shares	38,600
Granted, Shares	15,850
Granted, Weighted-Average Grant Date Fair Value	$ 20.57
Vested, Shares	(13,100)
Vested, Weighted-Average Grant Date Fair Value	$ 15.36
Balance at September 30, 2012	$ 20.82
Balance at September 30, 2012, Shares	41,350
PBRS [Member]
Summary of liability-based award activity
Balance at January 1, 2012	$ 15.36
Balance at January 1, 2012, Shares	1,956
Granted, Shares
Granted, Weighted-Average Grant Date Fair Value
Vested, Shares	(1,956)
Vested, Weighted-Average Grant Date Fair Value	$ 15.36
Balance at September 30, 2012
Balance at September 30, 2012, Shares
PUP Awards [Member]
Summary of liability-based award activity
Balance at January 1, 2012	$ 23.02
Balance at January 1, 2012, Shares	95,500
Granted, Shares	115,100
Granted, Weighted-Average Grant Date Fair Value	$ 20.60
Vested, Shares
Vested, Weighted-Average Grant Date Fair Value
Balance at September 30, 2012	$ 21.70
Balance at September 30, 2012, Shares	210,600