Allowance for loan losses (Details 2) (USD $) In Thousands, unless otherwise specified				3 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2011	Mar. 31, 2012 Covered Loans [Member]	Mar. 31, 2011 Covered Loans [Member]
Allowance for Covered Loan Losses:
Balance at beginning of the period	$ 103,849	$ 107,699	$ 114,690	$ 36,417	$ 13,733
Provision for loan losses before benefit attributable to FDIC loss share agreements				10,831	20,510
Benefit attributable to FDIC loss share agreements				(4,899)	(15,179)
Net provision for covered loan losses				5,932	5,331
Increase in indemnification asset				4,899	15,179
Loans charged-off				(6,178)	(5,838)
Balance at end of the period	$ 103,849	$ 107,699	$ 114,690	$ 41,070	$ 28,405