FEDERAL HOME LOAN BANK ADVANCES AND OTHER BORROWINGS - Financial Data of Federal Home Loan Bank Advances (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Banking and Thrift [Abstract]
Weighted-average interest rate at end of year	0.67%	0.40%	0.29%
Average interest rate during the year	0.49%	0.38%	0.20%
Average balance	$ 1,153,208	$ 553,162	$ 267,816
Maximum amount outstanding at any month-end	1,990,000	1,355,000	633,000
Balance at end of year	$ 490,000	$ 930,000	$ 633,000