GOODWILL, OTHER INTANGIBLE ASSETS AND MORTGAGE SERVICING RIGHTS (Finite-Lived Intangible Assets) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Finite-lived Intangible Assets [Roll Forward]
Goodwill, beginning of period	$ 244,583	$ 247,738
Goodwill and other intangibles, net, beginning of period	274,745	285,210
Amortization	(4,943)	(7,310)
Goodwill, Purchase Accounting Adjustments		3,155
Goodwill, end of period	244,583	244,583
Goodwill and other intangibles, net, end of period	269,802	274,745
Core Deposit Intangibles [Member]
Finite-lived Intangible Assets [Roll Forward]
Finite lived assets Balance, beginning of period	29,701	36,762
Amortization	(4,790)	(7,061)
Finite lived assets Balance, end of period	24,911	29,701
Leasehold Improvements [Member]
Finite-lived Intangible Assets [Roll Forward]
Finite lived assets Balance, beginning of period	461	710
Amortization	(153)	(249)
Finite lived assets Balance, end of period	$ 308	$ 461