Share-Based Compensation Plan (Details) (USD $)	12 Months Ended	0 Months Ended	12 Months Ended			0 Months Ended
	Dec. 31, 2012	Jan. 31, 2013 Restricted Stock [Member]	Dec. 31, 2012 Restricted Stock [Member]	Dec. 31, 2011 Restricted Stock [Member]	Dec. 31, 2010 Restricted Stock [Member]	Jan. 31, 2013 Performance Shares [Member]	Feb. 08, 2012 Performance Shares [Member]
Summary of restricted share activity
Unvested shares, Beginning balance			128,664	78,440	15,000
Unvested weighted average grant date fair value, beginning balance			$ 21.59	$ 20.88	$ 20.00
Unvested shares, Granted		59,245	52,545	79,330	70,110	72,118
Granted, weighted average grant date fair value			$ 23.15	$ 22.03	$ 20.98		$ 23.15
Vested, shares			(52,587)	(26,874)	(4,170)
Vested, weighted average grant date fair value			$ 21.43	$ 20.83	$ 20.00
Forfeited, shares	0			(2,232)	(2,500)
Forfeited, weighted average grant date fair value	$ 0.00			$ 21.58	$ 20.00
Unvested shares, Ending balance			128,622	128,664	78,440
Unvested weighted average grant date fair value, ending balance			$ 22.19	$ 21.59	$ 20.88