ACQUISITIONS - Narrative (Detail) $ / shares in Units, $ in Thousands			1 Months Ended	3 Months Ended			12 Months Ended
	Apr. 28, 2017 USD ($) Branch $ / shares shares	Apr. 29, 2016 USD ($) Branch $ / shares shares	Apr. 29, 2016 USD ($) Branch $ / shares	Sep. 30, 2017 USD ($)	Dec. 31, 2016 Branch	Mar. 31, 2016 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2018 USD ($)
Business Acquisition [Line Items]
Common stock issued in acquisitions							$ 0	$ 62,246	$ 165,295
Loans		$ 691,000	$ 691,000
Intangible assets assumed		17,000	17,000
Total consideration paid		164,000
Goodwill		66,000	66,000				$ 107,366	107,366
Fixed assets		63,000	63,000
Customer list intangibles
Business Acquisition [Line Items]
Intangible assets assumed										$ 290
Group of financial advisors
Business Acquisition [Line Items]
Common stock issued amount						$ 2,600
Value of cash consideration						800
Total consideration paid						4,900
Earn-out liability payable						1,500
Goodwill						400
Fixed assets						$ 200
Portion of customer intangible amortized by straight line method						10 years
Adjusted earn-out liability								2,400
Useful life of portion of customer intangible amortized						15 years
Group of financial advisors | Customer list intangibles
Business Acquisition [Line Items]
Intangible assets assumed						$ 4,300		$ 900
As recorded by Baylake Corp
Business Acquisition [Line Items]
Loans		710,000	710,000
Intangible assets assumed		1,000	1,000
Fixed assets		$ 71,000	$ 71,000
Merger Agreement | First Menasha
Business Acquisition [Line Items]
Number of branches | Branch	5
Number of branches closed | Branch	1
Number of common stock issued for consideration | shares	1,309,885
Number of common stock for each outstanding share of common stock	3.126
Common stock issued amount	$ 62,200
Price per share for stock issued in consideration | $ / shares	$ 47.52
Number of trading days	20 days
Value of cash consideration	$ 19,300
Direct stock issuance costs for the merger charged against additional paid in capital	200
Amount of addition in assets	480,000
Loans	351,000
Amount of addition in deposit	375,000
Amount of addition in goodwill	41,000			$ 41,000
Increase in goodwill				1,000
Gain in pre-tax earnings				$ 1,200
Merger Agreement | First Menasha | Core deposit intangibles
Business Acquisition [Line Items]
Intangible assets assumed	$ 4,000
Merger Agreement | As recorded by Baylake Corp
Business Acquisition [Line Items]
Number of branches | Branch			21
Number of branches closed | Branch		1			6
Number of common stock issued for consideration | shares		4,344,243
Number of common stock for each outstanding share of common stock		0.4517
Common stock issued in acquisitions		$ 163,300
Price per share for stock issued in consideration | $ / shares		$ 37.58	$ 37.58
Number of trading days		20 days
Direct stock issuance costs for the merger charged against additional paid in capital		$ 300
Additional consideration for assumed stock options		$ 1,200