GOODWILL AND OTHER INTANGIBLES - Gross Amount and Accumulated Amortization of Other Intangible Assets (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014	Jun. 30, 2012
Finite Lived Intangible Assets [Line Items]
Gross amount			$ 24,500
Goodwill And Intangible Assets Disclosure [Abstract]
Finite Lived Intangible Assets Amortization Expense Next Twelve Months	$ 1,326
Finite Lived Intangible Assets Amortization Expense Year Two	4,884
Finite Lived Intangible Assets Amortization Expense Year Three	4,270
Finite Lived Intangible Assets Amortization Expense Year Four	3,313
Finite Lived Intangible Assets Amortization Expense After Year Five	10,019
Core Deposits [Member]
Finite Lived Intangible Assets [Line Items]
Gross amount	45,844	$ 45,844
Finite lived Intangible Assets Acquired 1	5,820	0
Accumulated amortization	(41,939)	(40,424)
Net carrying amount	$ 9,725	$ 5,420
Remaining amortization period	9 years 3 months 18 days	8 years 4 months 24 days
Purchased Credit Card Relationship Intangible [Member]
Finite Lived Intangible Assets [Line Items]
Gross amount	$ 24,465	$ 24,465
Accumulated amortization	(10,378)	(8,076)
Net carrying amount	$ 14,087	$ 16,389
Remaining amortization period	6 years 1 month 6 days	6 years 10 months 24 days