GOODWILL, OTHER INTANGIBLE ASSETS AND MORTGAGE SERVICING RIGHTS (Finite-Lived Intangible Assets) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015		Dec. 31, 2014
Goodwill [Line Items]
Goodwill, beginning of period	$ 247,738	$ 0		$ 0
Intangible Assets, Net (Including Goodwill), beginning of period	285,210	2,831		2,449
Goodwill, Acquired During Period		247,738		0
Acquired Intangible Assets (Including Goodwill)		285,909		2,372
Amortization	(7,310)	(3,230)		(1,990)
Goodwill, Other Changes	(3,155)
Finite-Lived Intangible Assets, Other Changes	0	(300)	[1]
Intangible Assets (including Goodwill), Other Changes	(3,155)	(300)	[1]
Goodwill, end of period	244,583	247,738		0
Balance, end of period	29,701
Intangible Assets, Net (Including Goodwill), end of period	274,745	285,210		2,831
Core Deposit Intangibles [Member]
Goodwill [Line Items]
Balance, beginning of period	36,762	2,831		2,449
Additions through acquisition		37,395		2,372
Amortization	(7,061)	(3,164)		(1,990)
Balance, end of period	29,701	36,762		2,831
Other Intangible Assets [Member]
Goodwill [Line Items]
Balance, beginning of period	710	0
Additions through acquisition		776
Amortization	(249)	(66)
Balance, end of period	$ 461	$ 710		$ 0

[1] Acquired CDI from Starbuck was adjusted for a branch that was subsequently sold.