FEDERAL HOME LOAN BANK ADVANCES - Contractual Maturities and Weighted Average Interest Rates of FHLB Advances (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Contractual Maturity, Amount
Overnight		$ 185,000
2018	$ 265,000	315,083
2019	648	1,291
Total FHLB advances except overnight advances	265,648	316,374
Total FHLB advances	$ 265,648	$ 501,374
Weighted Average Rate
Overnight (as a percent)		1.53%
2018 (as a percent)	2.47%	1.59%
2019 (as a percent)	0.68%	0.94%
Weighted Average Rate for total FHLB advances except overnight advances (as a percent)	2.47%	1.59%
Weighted Average Rate for total FHLB advances (as a percent)	2.47%	1.57%