Fair Value of Financial Instruments - Estimated Fair Values and Carrying Amounts of Financial Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Financial Assets
Cash and cash equivalents	$ 1,301,118	$ 1,362,126	$ 996,655	$ 510,267
Loans and loans held for sale, net of unearned income and allowance for loan losses	15,254,535		14,643,789
Derivative instruments	34,172	38,886
Financial Liabilities
Deposits	17,312,265	17,408,283	$ 16,260,566
Short-term borrowings	448,696	509,136
Long-term debt	628,085	628,953
Derivative instruments	27,068	30,209
Level 1
Financial Assets
Cash and cash equivalents	1,301,118	1,362,126
Investment securities	0	0
Loans and loans held for sale, net of unearned income and allowance for loan losses	0	0
Derivative instruments	0	0
Financial Liabilities
Deposits	0	0
Short-term borrowings	368,696	334,136
Long-term debt	0	0
Derivative instruments	0	0
Level 2
Financial Assets
Cash and cash equivalents	0	0
Investment securities	3,910,766	3,536,029
Loans and loans held for sale, net of unearned income and allowance for loan losses	122,333	157,041
Derivative instruments	34,172	38,886
Financial Liabilities
Deposits	0	0
Short-term borrowings	80,000	175,000
Long-term debt	0	0
Derivative instruments	27,068	30,209
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	15,073,846	14,909,014
Derivative instruments	0	0
Financial Liabilities
Deposits	16,663,693	16,762,475
Short-term borrowings	0	0
Long-term debt	617,254	617,656
Derivative instruments	0	0
Carrying Amount
Financial Assets
Cash and cash equivalents	1,301,118	1,362,126
Investment securities	3,909,971	3,535,313
Loans and loans held for sale, net of unearned income and allowance for loan losses	15,109,645	15,077,293
Derivative instruments	34,172	38,886
Financial Liabilities
Deposits	17,312,265	17,408,283
Short-term borrowings	448,696	509,136
Long-term debt	628,085	628,953
Derivative instruments	27,068	30,209
Fair Value
Financial Assets
Cash and cash equivalents	1,301,118	1,362,126
Investment securities	3,910,766	3,536,029
Loans and loans held for sale, net of unearned income and allowance for loan losses	15,196,179	15,066,055
Derivative instruments	34,172	38,886
Financial Liabilities
Deposits	16,663,693	16,762,475
Short-term borrowings	448,696	509,136
Long-term debt	617,254	617,656
Derivative instruments	$ 27,068	$ 30,209