Fair Value of Financial Instruments - Estimated Fair Values and Carrying Amounts of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Financial Assets
Cash and cash equivalents	$ 626,516	$ 970,977
FDIC loss share receivable	284,471	423,069
Financial Liabilities
Deposits	10,686,267	10,748,277
Short-term borrowings	294,156	303,045
Long-term debt	323,046	423,377
Carrying Amount [Member]
Financial Assets
Cash and cash equivalents	626,516	970,977
Investment securities	2,149,990	1,950,067
Loans and loans held for sale	8,783,012	8,766,055
FDIC loss share receivable	284,471	423,069
Derivative instruments	41,208	42,119
Accrued interest receivable	32,707	32,183
Financial Liabilities
Deposits	10,686,267	10,748,277
Short-term borrowings	294,156	303,045
Long-term debt	323,046	423,377
Derivative instruments	34,383	36,890
Accrued interest payable	6,421	6,615
Fair Value [Member]
Financial Assets
Cash and cash equivalents	626,516	970,977
Investment securities	2,154,648	1,956,502
Loans and loans held for sale	8,902,016	8,800,563
FDIC loss share receivable	126,727	207,222
Derivative instruments	41,208	42,119
Accrued interest receivable	32,707	32,183
Financial Liabilities
Deposits	10,480,000	10,594,885
Short-term borrowings	294,156	303,045
Long-term debt	286,986	394,490
Derivative instruments	34,383	36,890
Accrued interest payable	$ 6,421	$ 6,615