Allowance for loan losses (Details 2) (USD $) In Thousands, unless otherwise specified				3 Months Ended		9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Sep. 30, 2012 Covered Loans [Member]	Sep. 30, 2011 Covered Loans [Member]	Sep. 30, 2012 Covered Loans [Member]	Sep. 30, 2011 Covered Loans [Member]	Mar. 31, 2011 Covered Loans [Member]
Allowance for Covered Loan Losses:
Balance at beginning of the period	$ 98,942	$ 107,699	$ 109,187	$ 42,606		$ 36,417	$ 13,733	$ 33,360
Provision for loan losses before benefit attributable to FDIC loss share agreements				7,698	12,992	28,177	48,657
Benefit attributable to FDIC loss share agreements				(1,484)	(8,224)	(12,601)	(31,077)
Net provision for covered loan losses				6,214	4,768	15,576	17,580
Increase in indemnification asset				1,484	8,224	12,601	31,077
Loans charged-off				(6,660)	(11,749)	(20,950)	(27,787)
Balance at end of the period	$ 98,942	$ 107,699	$ 109,187	$ 43,644	$ 34,603	$ 43,644	$ 34,603	$ 33,360