Loans Receivable - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Loans Receivable [Line Items]
Percentage of covered loan loss, covered under loss share agreements	80.00%
Number of acquisitions	4
Deferred loan origination fees	$ 14,082,000		$ 14,040,000
Deferred loan expenses	5,626,000		5,270,000
Deposit liabilities reclassified as loans receivable	2,411,000		3,231,000
Loans with carrying value pledged to secure public deposits and other borrowings	2,262,625,000		1,504,512,000
Valuation allowance against indemnification assets	31,813,000
Income tax expense (benefit)	(4,876,000)	7,134,000
Non-covered troubled debt restructurings modified during the current period	1,545,000	4,061,000
Total TDRs	18,508,000	27,339,000
CSB, Orion and Century [Member]
Loans Receivable [Line Items]
Percentage of covered loan losses that exceeds the contractual threshold, covered under loss share agreements	95.00%
Sterling Bank [Member]
Loans Receivable [Line Items]
Percentage of covered loan losses that exceeds the contractual threshold, covered under loss share agreements	80.00%
Troubled Debt Restructurings [Member]
Loans Receivable [Line Items]
Total TDRs	$ 18,508,000	$ 27,339,000