Share-Based Compensation Plan (Details) (Restricted Stock [Member], USD $)	3 Months Ended	12 Months Ended
	Dec. 31, 2009	Dec. 31, 2011	Dec. 31, 2010
Restricted Stock [Member]
Summary of restricted share activity
Unvested shares, Beginning balance	0	78,440	15,000
Unvested weighted average grant date fair value, beginning balance	$ 0.00	$ 20.88	$ 20.00
Unvested shares, Granted	15,000	79,330	70,110
Granted, weighted average grant date fair value	$ 20.00	$ 22.03	$ 20.98
Vested, shares		(26,874)	(4,170)
Vested, weighted average grant date fair value		$ 20.83	$ 20.00
Forfeited, shares		(2,232)	(2,500)
Forfeited, weighted average grant date fair value		$ 21.58	$ 20.00
Unvested shares, Ending balance	15,000	128,664	78,440
Unvested weighted average grant date fair value, ending balance	$ 20.00	$ 21.59	$ 20.88