Goodwill and Other Intangible Assets (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended			12 Months Ended	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013 Core Deposits Member	Dec. 31, 2012 Core Deposits Member	Mar. 31, 2013 Other Intangible Assets [Member]	Dec. 31, 2012 Other Intangible Assets [Member]
Summary of core deposit intangibles and other intangibles
Gross carrying amount			$ 41,831	$ 41,831	$ 19,283	$ 19,283
Accumulated amortization			(34,824)	(34,044)	(12,074)	(11,843)
Net book value			7,007	7,787	7,209	7,440
Amortization of other intangible assets	$ 1,011	$ 1,049	$ 780	$ 3,229	$ 231	$ 966