Fair Value of Financial Instruments - Estimated Fair Values and Carrying Amounts of Financial Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Financial Assets
Cash and cash equivalents	$ 682,272	$ 548,095	$ 668,007	$ 391,396
Loans and loans held for sale, net of unearned income and allowance for loan losses	14,319,187		11,229,417
FDIC loss share receivables	43,443	69,627	94,712	$ 162,312
Derivative instruments	30,086	28,798
Financial Liabilities
Deposits	16,303,065	12,520,525	$ 12,377,691
Short-term borrowings	222,460	845,742
Long-term debt	341,973	403,254
Derivative instruments	24,534	15,411
Level 1
Financial Assets
Cash and cash equivalents	682,272	548,095
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	222,460	845,742
Long-term debt	0	0
Derivative instruments	0	0
Level 2
Financial Assets
Cash and cash equivalents	0	0
Investment securities	2,928,416	2,278,334
Loans and loans held for sale, net of unearned income and allowance for loan losses	212,764	139,950
FDIC loss share receivables	0	0
Derivative instruments	41,440	32,903
Financial Liabilities
Deposits	0	0
Short-term borrowings	0	0
Long-term debt	0	0
Derivative instruments	38,147	31,354
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	14,424,343	11,335,365
FDIC loss share receivables	8,437	19,606
Derivative instruments	0	0
Financial Liabilities
Deposits	15,996,499	12,298,017
Short-term borrowings	0	0
Long-term debt	311,982	376,139
Derivative instruments	0	0
Carrying Amount
Financial Assets
Cash and cash equivalents	682,272	548,095
Investment securities	2,926,135	2,275,813
Loans and loans held for sale, net of unearned income and allowance for loan losses	14,188,933	11,450,985
FDIC loss share receivables	43,443	69,627
Derivative instruments	41,440	32,903
Financial Liabilities
Deposits	16,303,065	12,520,525
Short-term borrowings	222,460	845,742
Long-term debt	341,973	403,254
Derivative instruments	38,147	31,354
Fair Value
Financial Assets
Cash and cash equivalents	682,272	548,095
Investment securities	2,928,416	2,278,334
Loans and loans held for sale, net of unearned income and allowance for loan losses	14,637,107	11,475,315
FDIC loss share receivables	8,437	19,606
Derivative instruments	41,440	32,903
Financial Liabilities
Deposits	15,996,499	12,298,017
Short-term borrowings	222,460	845,742
Long-term debt	311,982	376,139
Derivative instruments	$ 38,147	$ 31,354