Fair Value of Financial Instruments - Estimated Fair Values and Carrying Amounts of Financial Instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Financial Assets
Cash and cash equivalents	$ 469,360	$ 1,362,126	$ 705,298	$ 510,267
Loans and loans held for sale, net of unearned income and allowance for loan losses	15,696,975		14,952,214
Derivative instruments	32,900	38,886
Financial Liabilities
Deposits	16,853,116	17,408,283	$ 15,862,027
Short-term borrowings	583,935	509,136
Long-term debt	667,243	628,953
Derivative instruments	28,684	30,209
Level 1
Financial Assets
Cash and cash equivalents	469,360	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	333,935	334,136
Long-term debt	0	0
Derivative instruments	0	0
Level 2
Financial Assets
Cash and cash equivalents	0	0
Investment securities	4,094,747	3,536,029
Loans and loans held for sale, net of unearned income and allowance for loan losses	140,959	157,041
Derivative instruments	32,900	38,886
Financial Liabilities
Deposits	0	0
Short-term borrowings	250,000	175,000
Long-term debt	0	0
Derivative instruments	28,684	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	15,526,610	14,909,014
Derivative instruments	0	0
Financial Liabilities
Deposits	15,817,343	16,762,475
Short-term borrowings	0	0
Long-term debt	658,483	617,656
Derivative instruments	0	0
Carrying Amount
Financial Assets
Cash and cash equivalents	469,360	1,362,126
Investment securities	4,093,816	3,535,313
Loans and loans held for sale, net of unearned income and allowance for loan losses	15,550,750	15,077,293
Derivative instruments	32,900	38,886
Financial Liabilities
Deposits	16,853,116	17,408,283
Short-term borrowings	583,935	509,136
Long-term debt	667,243	628,953
Derivative instruments	28,684	30,209
Fair Value
Financial Assets
Cash and cash equivalents	469,360	1,362,126
Investment securities	4,094,747	3,536,029
Loans and loans held for sale, net of unearned income and allowance for loan losses	15,667,569	15,066,055
Derivative instruments	32,900	38,886
Financial Liabilities
Deposits	15,817,343	16,762,475
Short-term borrowings	583,935	509,136
Long-term debt	658,483	617,656
Derivative instruments	$ 28,684	$ 30,209