Intangible Assets (Details 1) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Carrying amount, accumulated amortization and amortization expense of core deposit intangible assets
Carrying amount	$ 10,607	$ 12,327	$ 10,607	$ 12,327	$ 11,472
Amortization of intangible assets			2,068	1,904
Core deposit intangible assets [Member]
Carrying amount, accumulated amortization and amortization expense of core deposit intangible assets
Gross original amount	26,468	26,468	26,468	26,468	26,468
Accumulated amortization	19,324	17,825	19,324	17,825	18,589
Carrying amount	7,144	8,643	7,144	8,643	7,879
Amortization of intangible assets	$ 368	$ 381	$ 735	$ 763