GOODWILL AND OTHER INTANGIBLES - Gross Amount and Accumulated Amortization of Other Intangible Assets (Detail) - USD ($) $ in Thousands		1 Months Ended	3 Months Ended	12 Months Ended
		Feb. 27, 2015	Sep. 30, 2017	Dec. 31, 2016	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 Year Two			$ 3,591
Finite Lived Intangible Assets Amortization Expense Year Three			3,088
Finite Lived Intangible Assets Amortization Expense Year Four			2,851
Finite Lived Intangible Assets Amortization Expense After Year Five			2,066
Finite Lived Intangible Assets Amortization Expense Remainder Of Fiscal Year			1,077
Finite Lived Intangible Assets Amortization Expense Year Five			2,658
Core Deposits [Member]
Finite Lived Intangible Assets [Line Items]
Gross amount			51,664	$ 51,664
Finite lived Intangible Assets Acquired 1		$ 5,800		0
Accumulated amortization	[1]		(45,779)	(44,466)
Net carrying amount			$ 5,885	$ 7,198
Remaining amortization period			7 years 3 months 18 days	8 years 1 month 6 days
Purchased Credit Card Relationship Intangible [Member]
Finite Lived Intangible Assets [Line Items]
Gross amount			$ 24,465	$ 24,465
Accumulated amortization	[2]		(15,832)	(13,934)
Net carrying amount			$ 8,633	$ 10,531
Remaining amortization period			4 years 2 months 12 days	5 years
Customer Related Intangible Assets [Member]
Finite Lived Intangible Assets [Line Items]
Gross amount			$ 1,067	$ 1,067
Accumulated amortization	[3]		(254)	(140)
Net carrying amount			$ 813	$ 927
Remaining amortization period			5 years 3 months 18 days	6 years 1 month 6 days

[1] (1) For the quarter and nine-month period ended September 30, 2017, the amortization expense of core deposit intangibles amounted to $0.4 million and $1.3 million, respectively (2016 - $0.5 million and $1.5 million, respectively).

[2] (2) For the quarter and nine-month period ended September 30, 2017, the amortization expense of the purchased credit card relationship intangible amounted to $0.6 million and $1.9 million, respectively (2016 - $0.7 million and $2.1 million, respectively).

[3] (3) For the quarter and nine-month period ended September 30, 2017, the amortization expense of insurance customer relationship intangible amounted to $38 thousand and $0.1 million, respectively (2016 - $38 thousand and $0.1 million, respectively).