Allowance for Credit Losses - Allowance for Credit Losses (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended	12 Months Ended				3 Months Ended		9 Months Ended					3 Months Ended		9 Months Ended					3 Months Ended		9 Months Ended					3 Months Ended		9 Months Ended
	Sep. 30, 2012 quarter	Sep. 30, 2011	Sep. 30, 2012 quarter	Dec. 31, 2011	Jun. 30, 2012 quarter	Mar. 31, 2012	Mar. 31, 2011	Sep. 30, 2012 Commercial	Sep. 30, 2011 Commercial	Sep. 30, 2012 Commercial	Sep. 30, 2011 Commercial	Mar. 31, 2012 Commercial	Dec. 31, 2011 Commercial	Mar. 31, 2011 Commercial	Sep. 30, 2012 Real Estate Portfolio Segment	Sep. 30, 2011 Real Estate Portfolio Segment	Sep. 30, 2012 Real Estate Portfolio Segment	Sep. 30, 2011 Real Estate Portfolio Segment	Mar. 31, 2012 Real Estate Portfolio Segment	Dec. 31, 2011 Real Estate Portfolio Segment	Mar. 31, 2011 Real Estate Portfolio Segment	Sep. 30, 2012 Consumer	Sep. 30, 2011 Consumer	Sep. 30, 2012 Consumer	Sep. 30, 2011 Consumer	Mar. 31, 2012 Consumer	Dec. 31, 2011 Consumer	Mar. 31, 2011 Consumer	Sep. 30, 2012 Unallocated	Sep. 30, 2011 Unallocated	Sep. 30, 2012 Unallocated	Sep. 30, 2011 Unallocated	Mar. 31, 2012 Unallocated	Dec. 31, 2011 Unallocated	Mar. 31, 2011 Unallocated
Financing Receivable, Allowance for Credit Losses [Line Items]
Lookback period used in reserve analysis	16		16		12
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance for credit losses, beginning balance			$ 11,396	$ 11,014		$ 10,140	$ 11,035			$ 2,266	$ 2,437	$ 2,799		$ 2,926			$ 7,155	$ 5,836	$ 5,474		$ 5,508			$ 1,836	$ 2,503	$ 1,494		$ 1,296			$ 139	$ 238	$ 373		$ 1,305
Provision charged to operations	0	400	500	750				(329)	(179)	33	376				532	965	643	610				151	690	(56)	(227)				(354)	(1,076)	(120)	(9)
Losses charged to allowance	(220)	(725)	(2,401)	(1,466)				(1)	(38)	(123)	(254)				0	(286)	(1,792)	(312)				(219)	(401)	(486)	(900)				0	0	0	0
Recoveries	294	321	719	733				209	69	502	219				0	175	0	228				85	77	217	286				0	0	0	0
Allowance for credit losses, ending balance	10,214	11,031	10,214	11,396		10,140	11,035	2,678	2,778	2,678	2,778	2,799		2,926	6,006	6,362	6,006	6,362	5,474		5,508	1,511	1,662	1,511	1,662	1,494		1,296	19	229	19	229	373		1,305
Ending balance: individually evaluated for impairment	965		965	4,368				42		42			231		909		909			3,764		14		14			373		0		0			0
Ending balance: collectively evaluated for impairment	$ 9,249		$ 9,249	$ 7,028				$ 2,636		$ 2,636			$ 2,035		$ 5,097		$ 5,097			$ 3,391		$ 1,497		$ 1,497			$ 1,463		$ 19		$ 19			$ 139