OFF-BALANCE SHEET ARRANGEMENTS, COMMITMENTS AND CONTINGENCIES - Future Cash Payments Associated With Contractual Obligations (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Certificates and other time deposits
1 year or less	$ 1,001,668
More than 1 year but less than 3 years	274,123
3 years or more but less than 5 years	44,251
Total	1,320,042	$ 1,262,332
Federal Home Loan Bank advances
1 year or less	365,502
More than 1 year but less than 3 years	50,874
Total	416,376
Subordinated debentures and subordinated notes
1 year or less	4,019
More than 1 year but less than 3 years	3,884
3 years or more but less than 5 years	10,077
5 years or more	82,560
Total	100,540
Operating leases
1 year or less	1,690
More than 1 year but less than 3 years	2,587
3 years or more but less than 5 years	1,781
5 years or more	2,493
Total	8,551
Total
1 year or less	1,372,879
More than 1 year but less than 3 years	331,468
3 years or more but less than 5 years	56,109
5 years or more	85,053
Total	1,845,509
Interest payments on Federal Home Loan Bank advances to be paid over future periods.	4,400
Interest included in payments for subordinated debentures	$ 43,400