Fair Value of Financial Instruments - Estimated Fair Values and Carrying Amounts of Financial Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Financial Assets
Cash and cash equivalents	$ 996,655	$ 510,267	$ 967,290	$ 548,095
Loans and loans held for sale, net of unearned income and allowance for loan losses	14,643,789		13,088,505
FDIC loss share receivables	33,564	39,878	60,972	$ 69,627
Derivative instruments	40,037	24,393
Financial Liabilities
Deposits	16,260,566	16,178,748	$ 14,665,024
Short-term borrowings	498,238	326,617
Long-term debt	598,924	340,447
Derivative instruments	39,540	18,058
Level 1
Financial Assets
Cash and cash equivalents	996,655	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	498,238	326,617
Long-term debt	0	0
Derivative instruments	0	0
Level 2
Financial Assets
Cash and cash equivalents	0	0
Investment securities	2,854,464	2,901,247
Loans and loans held for sale, net of unearned income and allowance for loan losses	192,545	166,247
FDIC loss share receivables	0	0
Derivative instruments	48,594	30,486
Financial Liabilities
Deposits	0	0
Short-term borrowings	0	0
Long-term debt	0	0
Derivative instruments	48,772	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	14,602,056	14,508,502
FDIC loss share receivables	6,282	9,163
Derivative instruments	0	0
Financial Liabilities
Deposits	16,090,782	15,696,245
Short-term borrowings	0	0
Long-term debt	563,571	309,847
Derivative instruments	0	0
Carrying Amount
Financial Assets
Cash and cash equivalents	996,655	510,267
Investment securities	2,851,542	2,899,214
Loans and loans held for sale, net of unearned income and allowance for loan losses	14,497,232	14,355,297
FDIC loss share receivables	33,564	39,878
Derivative instruments	48,594	30,486
Financial Liabilities
Deposits	16,260,566	16,178,748
Short-term borrowings	498,238	326,617
Long-term debt	598,924	340,447
Derivative instruments	48,772	24,939
Fair Value
Financial Assets
Cash and cash equivalents	996,655	510,267
Investment securities	2,854,464	2,901,247
Loans and loans held for sale, net of unearned income and allowance for loan losses	14,794,601	14,674,749
FDIC loss share receivables	6,282	9,163
Derivative instruments	48,594	30,486
Financial Liabilities
Deposits	16,090,782	15,696,245
Short-term borrowings	498,238	326,617
Long-term debt	563,571	309,847
Derivative instruments	$ 48,772	$ 24,939