Allowance for loan losses (Details Textuals) (USD $)	3 Months Ended		6 Months Ended		12 Months Ended				6 Months Ended		3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 31, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010	Jun. 30, 2011 Acquired Impaired Loans [Member]	Dec. 31, 2010 Acquired Impaired Loans [Member]	Jun. 30, 2010 Acquired Impaired Loans [Member]	Jun. 30, 2011 Acquired Non-Impaired Loans [Member]	Jun. 30, 2011 Loans With No Related Allowance [Member]	Jun. 30, 2011 Covered Loans [Member]	Jun. 30, 2010 Covered Loans [Member]	Jun. 30, 2011 Covered Loans [Member]	Jun. 30, 2010 Covered Loans [Member]	Dec. 31, 2010 Covered Loans [Member]
Allowance for loan losses (Textuals) [Abstract]
Nonperforming Substandard loan outstanding			$ 300,000
Nonperforming Substandard doubtful loan outstanding			100,000
Increase in allowance for covered loan losses		0	33,360,000	0	13,733,000						33,400,000		33,400,000
Provision for loan losses	15,200,000	20,366,000		45,859,000	83,783,000				900,000		7,481,000	268,000	12,812,000	268,000	4,432,000
Increased in loss share receivable	7,700,000
Maturity of concessionary modification classified troubled debt restructurings			Less than 90 days
Trouble debt restructurings on acquired impaired loans						51,000,000	37,200,000	0
Financing Receivable, Modifications, Recorded Investment		61,400,000	41,900,000	61,400,000	46,800,000
Impaired loans			92,237,000		128,343,000					73,900,000
Allowance associated, Impaired Loans			$ 6,416,000		$ 6,181,000					$ 9,600,000