FDIC loss share (expense) income - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
F D I C Loss Share Expense Income [Line Items]
Estimated Credit Losses	$ 102,900,000		$ 102,900,000
Reversal of accelerated FDIC Indemnification Asset, Accretion of Discount	$ 15,046,000	$ 0	$ 15,046,000	$ 0
Federal Deposit Insurance Corporation [Member]
F D I C Loss Share Expense Income [Line Items]
Loss Sharing Agreement Allocation Percentage	80.00%