Loans (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2015 USD ($) bank	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Accounts, Notes, Loans and Financing Receivable
Failed banks acquired since 2009 | bank	6
Deferred loan origination fees	$ 26.3		$ 20.6
Deferred loan expenses	10.7		9.4
Deposit liabilities reclassified as loans receivable	5.2		5.6
Loans with carrying value pledged to secure public deposits and other borrowings	$ 4,000.0		$ 3,100.0
Carrying amounts of loans acquired		$ 2,200.0
Threshold period for loans in default	30 days
Troubled Debt Restructurings
Accounts, Notes, Loans and Financing Receivable
Total TDRs	$ 48.6
Energy related TDR	3.4
Accrual status TDR	$ 21.8
Florida Bank Group, Inc.
Accounts, Notes, Loans and Financing Receivable
Acquired loans		300.0
Old Florida Bancshares, Inc.
Accounts, Notes, Loans and Financing Receivable
Acquired loans		1,100.0
Georgia Commerce
Accounts, Notes, Loans and Financing Receivable
Acquired loans		800.0
Loans Acquired Without Deteriorated Credit Quality
Accounts, Notes, Loans and Financing Receivable
Carrying amounts of loans acquired		2,100.0
Loans Acquired With Deteriorated Credit Quality
Accounts, Notes, Loans and Financing Receivable
Carrying amounts of loans acquired		$ 41.1