Income Taxes (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Components of income tax expense attributable to continuing operations [Abstract]
Current tax expense									$ 11,054,000	$ 4,692,000	$ 9,667,000
Deferred tax expense (benefit)									(3,198,000)	2,419,000	2,130,000
Total	2,153,000	2,359,000	1,173,000	2,171,000	1,898,000	1,581,000	1,745,000	1,887,000	7,856,000	7,111,000	11,797,000
Reconciliation between statutory federal income tax and effective tax [Abstract]
Income tax expense at federal statutory rate									8,645,000	8,072,000	13,079,000
Federal tax credits									(480,000)	(480,000)	(480,000)
Interest income on tax-exempt securities									(512,000)	(471,000)	(372,000)
Other									203,000	(10,000)	(430,000)
Total	2,153,000	2,359,000	1,173,000	2,171,000	1,898,000	1,581,000	1,745,000	1,887,000	7,856,000	7,111,000	11,797,000
Reconciliation between statutory federal income tax rate and effective tax rate [Abstract]
Income tax expense at federal statutory rate (in hundredths)									35.00%	35.00%	35.00%
Federal tax credits (in hundredths)									(1.90%)	(2.10%)	(1.30%)
Interest income on tax-exempt securities (in hundredths)									(2.10%)	(2.00%)	(1.00%)
Other (in hundredths)									0.80%	(0.10%)	(1.10%)
Total (in hundredths)									31.80%	30.80%	31.60%
Future federal tax credits	3,100,000								3,100,000
Deferred tax assets [Abstract]
Covered assets	19,877,000				30,147,000				19,877,000	30,147,000
Allowance for loan losses	7,139,000				6,621,000				7,139,000	6,621,000
Deferred compensation	473,000				401,000				473,000	401,000
Other	848,000				974,000				848,000	974,000
Total deferred tax assets	28,337,000				38,143,000				28,337,000	38,143,000
Deferred tax liabilities [Abstract]
FDIC indemnification asset	13,943,000				24,566,000				13,943,000	24,566,000
Deferred loan fees	1,518,000				1,541,000				1,518,000	1,541,000
Premises and equipment	629,000				672,000				629,000	672,000
FHLB stock dividend	152,000				152,000				152,000	152,000
Investment in partnership	1,092,000				896,000				1,092,000	896,000
Prepaid expenses	217,000				163,000				217,000	163,000
Fair value adjustment of investment securities available for sale	2,531,000				1,704,000				2,531,000	1,704,000
Purchase accounting	6,451,000				8,993,000				6,451,000	8,993,000
Other	54,000				77,000				54,000	77,000
Total deferred tax liabilities	26,587,000				38,764,000				26,587,000	38,764,000
Deferred tax assets (liabilities), net	1,750,000				(621,000)				1,750,000	(621,000)
Valuation allowance for deferred tax assets	$ 0				$ 0				$ 0	$ 0