FAIR VALUE MEASUREMENTS - Financial Instruments (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 386,329	$ 479,443	$ 450,383	$ 371,407
Securities available for sale	2,927,463	2,764,562
Securities held to maturity	3,224,000	3,242,268
Securities held to maturity, fair value	3,131,964	3,218,379
Derivative assets	20,292	30,547
Deposits	22,497,089	22,399,725
Short-term borrowings	3,802,480	3,678,337
Long-term borrowings	659,890	668,173
Derivative liabilities	51,892	29,197
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	386,329	479,443
Securities available for sale	2,927,463	2,764,562
Securities held to maturity	3,224,000	3,242,268
Net loans and leases	21,121,132	20,916,277
Loan servicing rights	35,853	34,111
Marketable securities, equity securities	1,121
Derivative assets	20,292	30,547
Accrued interest receivable	95,082	94,254
Deposits	22,497,089	22,399,725
Short-term borrowings	3,802,480	3,678,337
Long-term borrowings	659,890	668,173
Derivative liabilities	51,892	29,197
Accrued interest payable	12,762	12,480
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, fair value	386,329	479,443
Securities available for sale	2,927,463	2,764,562
Securities held to maturity, fair value	3,131,964	3,218,379
Net loans and leases, fair value	20,900,639	20,661,196
Loan servicing rights, fair value	41,878	37,758
Marketable securities, equity securities, fair value	1,121
Derivative assets	20,292	30,547
Accrued interest receivable	95,082	94,254
Deposits, fair value	22,441,017	22,359,182
Short-term borrowings, fair value	3,802,988	3,678,723
Long-term borrowings, fair value	663,085	675,489
Derivative liabilities	51,892	29,197
Accrued interest payable	12,762	12,480
Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, fair value	386,329	479,443
Securities available for sale	0	161
Securities held to maturity, fair value	0	0
Net loans and leases, fair value	0	0
Loan servicing rights, fair value	0	0
Marketable securities, equity securities, fair value	177
Derivative assets	0	0
Accrued interest receivable	95,082	94,254
Deposits, fair value	17,755,830	17,779,246
Short-term borrowings, fair value	3,802,988	3,678,723
Long-term borrowings, fair value	0	0
Derivative liabilities	0	0
Accrued interest payable	12,762	12,480
Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, fair value	0	0
Securities available for sale	2,927,463	2,764,401
Securities held to maturity, fair value	3,131,964	3,218,379
Net loans and leases, fair value	21,610	56,458
Loan servicing rights, fair value	0	0
Marketable securities, equity securities, fair value	944
Derivative assets	18,912	28,953
Accrued interest receivable	0	0
Deposits, fair value	4,685,187	4,579,936
Short-term borrowings, fair value	0	0
Long-term borrowings, fair value	0	0
Derivative liabilities	51,887	29,192
Accrued interest payable	0	0
Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, fair value	0	0
Securities available for sale	0	0
Securities held to maturity, fair value	0	0
Net loans and leases, fair value	20,879,029	20,604,738
Loan servicing rights, fair value	41,878	37,758
Marketable securities, equity securities, fair value	0
Derivative assets	1,380	1,594
Accrued interest receivable	0	0
Deposits, fair value	0	0
Short-term borrowings, fair value	0	0
Long-term borrowings, fair value	663,085	675,489
Derivative liabilities	5	5
Accrued interest payable	$ 0	$ 0