Loans Receivable - Schedule of Non-Covered Loans Outstanding (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Loans Receivable [Line Items]
Total non-covered loans receivable	$ 7,590,802	$ 7,405,824
Non-Covered Loans [Member]
Loans Receivable [Line Items]
Total non-covered loans receivable	7,590,802	7,405,824
Non-Covered Loans [Member] | Residential Mortgage Loans [Member]
Loans Receivable [Line Items]
Total non-covered loans receivable	301,289	290,040
Non-Covered Loans [Member] | Residential Mortgage Loans [Member] | Residential 1-4 Family [Member]
Loans Receivable [Line Items]
Total non-covered loans receivable	296,175	284,019
Non-Covered Loans [Member] | Residential Mortgage Loans [Member] | Construction/ Owner Occupied [Member]
Loans Receivable [Line Items]
Total non-covered loans receivable	5,114	6,021
Non-Covered Loans [Member] | Commercial Loans [Member]
Loans Receivable [Line Items]
Total non-covered loans receivable	5,554,683	5,441,367
Non-Covered Loans [Member] | Commercial Loans [Member] | Real Estate [Member]
Loans Receivable [Line Items]
Total non-covered loans receivable	3,020,071	2,990,700
Non-Covered Loans [Member] | Commercial Loans [Member] | Business [Member]
Loans Receivable [Line Items]
Total non-covered loans receivable	2,534,612	2,450,667
Non-Covered Loans [Member] | Consumer And Other Loans [Member]
Loans Receivable [Line Items]
Total non-covered loans receivable	1,734,830	1,674,417
Non-Covered Loans [Member] | Consumer And Other Loans [Member] | Indirect Automobile [Member]
Loans Receivable [Line Items]
Total non-covered loans receivable	342,117	327,985
Non-Covered Loans [Member] | Consumer And Other Loans [Member] | Home Equity [Member]
Loans Receivable [Line Items]
Total non-covered loans receivable	1,092,693	1,076,913
Non-Covered Loans [Member] | Consumer And Other Loans [Member] | Other [Member]
Loans Receivable [Line Items]
Total non-covered loans receivable	$ 300,020	$ 269,519