FEDERAL HOME LOAN BANK ADVANCES - SHORT-TERM FHLB ADVANCES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
FHLB advances
Federal Home Loan Bank advances	$ 802,500	$ 699,500
Interest rate (as percent)	1.35%
Federal Home Loan Bank overnight advances
FHLB advances
Federal Home Loan Bank advances	$ 285,000	150,000
Average outstanding balance during the period	$ 91,087	$ 63,327	$ 15,756
Average interest rate during the year (as percent)	0.43%	0.17%	0.20%
Maximum outstanding at any month end during the period	$ 495,000	$ 387,000	$ 198,000
Federal Home Loan Bank overnight advances | Weighted Average
FHLB advances
Interest rate (as percent)	0.64%	0.35%