DEPOSITS - Types and Components of Deposit Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Noninterest bearing demand deposits:
Noninterest bearing demand deposits	$ 994,680	$ 1,037,401
Interest bearing deposits:
Total interest bearing deposits	3,430,350	3,478,046
Total deposits	4,425,030	4,515,447
Private accounts
Noninterest bearing demand deposits:
Noninterest bearing demand deposits	967,096	995,685
Interest bearing deposits:
Savings deposits	360,007	356,857
Money market demand deposits	440,442	443,015
Platinum money market deposits	344,546	308,105
Interest bearing checking	662,911	686,816
NOW demand deposits	23,451	20,142
Certificates and other time deposits, $250,000 or more	84,564	87,195
Certificates and other time deposits under $250,000	680,282	534,220
Total interest bearing deposits	2,596,203	2,436,350
Public accounts
Noninterest bearing demand deposits:
Noninterest bearing demand deposits	27,584	41,716
Interest bearing deposits:
Savings deposits	320	304
Money market demand deposits	15,513	19,560
Platinum money market deposits	329,695	360,006
Interest bearing checking	56,694	55,902
NOW demand deposits	141,200	114,401
Certificates and other time deposits, $250,000 or more	281,204	462,941
Certificates and other time deposits under $250,000	9,521	28,582
Total interest bearing deposits	$ 834,147	$ 1,041,696