Fair Value of Financial Instruments - Estimated Fair Values and Carrying Amounts of Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Financial Assets
Cash and cash equivalents	$ 881,216	$ 1,362,126	$ 1,101,253	$ 510,267
Loans and loans held for sale, net of unearned income and allowance for loan losses	19,936,303		15,135,365
Derivative instruments	31,779	38,886
Financial Liabilities
Deposits	21,334,271	17,408,283	$ 16,522,517
Short-term borrowings	1,523,704	509,136
Long-term debt	1,127,584	628,953
Derivative instruments	28,453	30,209
Level 1
Financial Assets
Cash and cash equivalents	881,216	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	548,696	334,136
Long-term debt	0	0
Derivative instruments	0	0
Level 2
Financial Assets
Cash and cash equivalents	0	0
Investment securities	4,912,654	3,536,029
Loans and loans held for sale, net of unearned income and allowance for loan losses	141,218	157,041
Derivative instruments	31,779	38,886
Financial Liabilities
Deposits	0	0
Short-term borrowings	975,008	175,000
Long-term debt	0	0
Derivative instruments	28,453	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	19,669,313	14,909,014
Derivative instruments	0	0
Financial Liabilities
Deposits	21,333,374	16,762,475
Short-term borrowings	0	0
Long-term debt	1,114,132	617,656
Derivative instruments	0	0
Carrying Amount
Financial Assets
Cash and cash equivalents	881,216	1,362,126
Investment securities	4,912,245	3,535,313
Loans and loans held for sale, net of unearned income and allowance for loan losses	19,799,675	15,077,293
Derivative instruments	31,779	38,886
Financial Liabilities
Deposits	21,334,271	17,408,283
Short-term borrowings	1,523,704	509,136
Long-term debt	1,127,584	628,953
Derivative instruments	28,453	30,209
Fair Value
Financial Assets
Cash and cash equivalents	881,216	1,362,126
Investment securities	4,912,654	3,536,029
Loans and loans held for sale, net of unearned income and allowance for loan losses	19,810,531	15,066,055
Derivative instruments	31,779	38,886
Financial Liabilities
Deposits	21,333,374	16,762,475
Short-term borrowings	1,523,704	509,136
Long-term debt	1,114,132	617,656
Derivative instruments	$ 28,453	$ 30,209