Fair Value of Financial Instruments - Estimated Fair Values and Carrying Amounts of Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2014
Financial Assets
Cash and cash equivalents	$ 1,101,253	$ 510,267	$ 682,272	$ 548,095
Loans and loans held for sale, net of unearned income and allowance for loan losses	15,135,365		14,319,187
FDIC loss share receivables	24,406	39,878	43,443	$ 69,627
Derivative instruments	47,436	24,393
Financial Liabilities
Deposits	16,522,517	16,178,748	$ 16,303,065
Short-term borrowings	713,272	326,617
Long-term debt	672,438	340,447
Derivative instruments	49,212	18,058
Level 1
Financial Assets
Cash and cash equivalents	1,101,253	510,267
Investment securities	0	0
Loans and loans held for sale, net of unearned income and allowance for loan losses	0	0
FDIC loss share receivables	0	0
Derivative instruments	0	0
Financial Liabilities
Deposits	0	0
Short-term borrowings	353,272	216,617
Long-term debt	0	0
Derivative instruments	0	0
Level 2
Financial Assets
Cash and cash equivalents	0	0
Investment securities	2,978,823	2,901,247
Loans and loans held for sale, net of unearned income and allowance for loan losses	210,866	166,247
FDIC loss share receivables	0	0
Derivative instruments	55,804	30,486
Financial Liabilities
Deposits	0	0
Short-term borrowings	360,000	110,000
Long-term debt	0	0
Derivative instruments	58,939	24,939
Level 3
Financial Assets
Cash and cash equivalents	0	0
Investment securities	0	0
Loans and loans held for sale, net of unearned income and allowance for loan losses	14,822,094	14,508,502
FDIC loss share receivables	6,343	9,163
Derivative instruments	0	0
Financial Liabilities
Deposits	16,485,224	15,696,245
Short-term borrowings	0	0
Long-term debt	660,140	309,847
Derivative instruments	0	0
Carrying Amount
Financial Assets
Cash and cash equivalents	1,101,253	510,267
Investment securities	2,976,066	2,899,214
Loans and loans held for sale, net of unearned income and allowance for loan losses	14,987,172	14,355,297
FDIC loss share receivables	24,406	39,878
Derivative instruments	55,804	30,486
Financial Liabilities
Deposits	16,522,517	16,178,748
Short-term borrowings	713,272	326,617
Long-term debt	672,438	340,447
Derivative instruments	58,939	24,939
Fair Value
Financial Assets
Cash and cash equivalents	1,101,253	510,267
Investment securities	2,978,823	2,901,247
Loans and loans held for sale, net of unearned income and allowance for loan losses	15,032,960	14,674,749
FDIC loss share receivables	6,343	9,163
Derivative instruments	55,804	30,486
Financial Liabilities
Deposits	16,485,224	15,696,245
Short-term borrowings	713,272	326,617
Long-term debt	660,140	309,847
Derivative instruments	$ 58,939	$ 24,939