ALLOWANCE FOR LOAN AND LEASE LOSSES - Changes in Allowance for Loan and Lease Losses (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016		Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning balance	$ 240,710		$ 222,395
Charge-offs	(26,535)		(32,013)
Recoveries	2,897		2,712
Provision For Loan Lease And Other Losses	21,053		32,970
Ending balance	238,125		226,064
Balance at end of period	81,495		62,140
Allowance for loan losses Purchased Credit Impaired	4,568		0
Ending balance: general allowance	152,062		163,924
Ending balance	9,131,342		9,485,372
Ending balance: impaired loans	917,591		954,981	$ 806,509	$ 945,407
Ending balance: purchased credit-impaired loans	172,332		181,114
Ending balance: loans with general allowance	8,041,419		8,349,277
Purchased Credit Impaired [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for loan losses Purchased Credit Impaired	4,568	[1]	0
Ending balance: purchased credit-impaired loans	172,332		181,114
Residential Mortgage [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning balance	39,570		27,301
Charge-offs	(7,306)		(5,192)
Recoveries	346		98
Provision For Loan Lease And Other Losses	5,938		6,475
Ending balance	38,548		28,682
Balance at end of period	16,150		14,862
Ending balance: general allowance	17,975		13,820
Ending balance	3,330,945		3,331,620
Ending balance: impaired loans	461,606		429,526
Ending balance: loans with general allowance	2,700,149		2,724,493
Residential Mortgage [Member] | Purchased Credit Impaired [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for loan losses Purchased Credit Impaired	4,423	[1]	0
Ending balance: purchased credit-impaired loans	169,190		177,601
Commercial Mortgage [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning balance	68,211		50,894
Charge-offs	(575)		(4,006)
Recoveries	46		276
Provision For Loan Lease And Other Losses	1,062		(2,137)
Ending balance	68,744		45,027
Balance at end of period	36,007		13,238
Ending balance: general allowance	32,592		31,789
Ending balance	1,524,491		1,649,263
Ending balance: impaired loans	191,251		224,365
Ending balance: loans with general allowance	1,330,098		1,421,619
Commercial Mortgage [Member] | Purchased Credit Impaired [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for loan losses Purchased Credit Impaired	145	[1]	0
Ending balance: purchased credit-impaired loans	3,142		3,279
Commercial And Industrial Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning balance	68,768		63,721
Charge-offs	(3,759)		(4,453)
Recoveries	280		558
Provision For Loan Lease And Other Losses	5,809		10,353
Ending balance	71,098		70,179
Balance at end of period	18,749		24,871
Ending balance: general allowance	52,349		45,308
Ending balance	2,343,416		2,442,867
Ending balance: impaired loans	168,160		226,656
Ending balance: loans with general allowance	2,175,256		2,216,211
Commercial And Industrial Loans [Member] | Purchased Credit Impaired [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for loan losses Purchased Credit Impaired	0	[1]	0
Ending balance: purchased credit-impaired loans	0		0
Construction Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning balance	3,519		12,822
Charge-offs	(91)		(605)
Recoveries	17		207
Provision For Loan Lease And Other Losses	(432)		1,215
Ending balance	3,013		13,639
Balance at end of period	1,202		3,381
Ending balance: general allowance	1,811		10,258
Ending balance	146,129		124,440
Ending balance: impaired loans	52,938		37,593
Ending balance: loans with general allowance	93,191		86,847
Construction Loans [Member] | Purchased Credit Impaired [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for loan losses Purchased Credit Impaired	0	[1]	0
Ending balance: purchased credit-impaired loans	0		0
Consumer Loan [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning balance	60,642		67,657
Charge-offs	(14,804)		(17,757)
Recoveries	2,208		1,573
Provision For Loan Lease And Other Losses	8,676		17,064
Ending balance	56,722		68,537
Balance at end of period	9,387		5,788
Ending balance: general allowance	47,335		62,749
Ending balance	1,786,361		1,937,182
Ending balance: impaired loans	43,636		36,841
Ending balance: loans with general allowance	1,742,725		1,900,107
Consumer Loan [Member] | Purchased Credit Impaired [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for loan losses Purchased Credit Impaired	0	[1]	0
Ending balance: purchased credit-impaired loans	$ 0		$ 234

[1] (1) Refer to Note 6 - Loans Held for Investment-PCI loans for a detail of changes in the allowance for loan losses related to PCI loans.