OFF-BALANCE SHEET ARRANGEMENTS, COMMITMENTS AND CONTINGENCIES - Future Cash Payments Associated With Contractual Obligations (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Certificates and other time deposits
1 year or less	$ 925,088
More than 1 year but less than 3 years	296,857
3 years or more but less than 5 years	44,512
Total	1,266,457	$ 1,262,332
Federal Home Loan Bank advances
1 year or less	232,012
Total	232,012
Subordinated debentures and subordinated notes
1 year or less	4,727
More than 1 year but less than 3 years	3,859
3 years or more but less than 5 years	7,726
5 years or more	85,396
Total	101,708
Operating leases
1 year or less	1,859
More than 1 year but less than 3 years	2,712
3 years or more but less than 5 years	1,849
5 years or more	2,702
Total	9,122
Total
1 year or less	1,163,686
More than 1 year but less than 3 years	303,428
3 years or more but less than 5 years	54,087
5 years or more	88,098
Total	1,609,299
Interest payments on Federal Home Loan Bank advances to be paid over future periods.	2,000
Interest included in payments for subordinated debentures	$ 44,500