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ACCOUNTING POLICIES (Details) $ in Thousands	3 Months Ended		9 Months Ended
ACCOUNTING POLICIES (Details) $ in Thousands	Sep. 30, 2018 USD ($) Type	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) Type	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Investment Securities [Abstract]
Unrealized gain on equity securities	$ 800
Wealth Management Services [Abstract]
Number of types of performance obligations \| Type	2		2
Contract Balances [Abstract]
Accounts receivable	$ 26,900		$ 26,900		$ 29,800
Unbilled fee revenue	7,900		7,900		6,500
Unearned revenue	2,900		2,900		3,900
Recently Adopted Accounting Pronouncements [Abstract]
Reclassification of other comprehensive income to retained earnings					0
Salaries and employee benefits	51,062	$ 48,426	155,323	$ 137,897
Other expenses	5,188	6,052	14,793	16,078
Retained Earnings [Member]
Recently Adopted Accounting Pronouncements [Abstract]
Reclassification of other comprehensive income to retained earnings					208
Accumulated Other Comprehensive Loss [Member]
Recently Adopted Accounting Pronouncements [Abstract]
Reclassification of other comprehensive income to retained earnings					$ (208)
ASU 2017-07 [Member]
Recently Adopted Accounting Pronouncements [Abstract]
Salaries and employee benefits		(1,900)		(5,100)
Other expenses		$ 1,900		$ 5,100
ASU 2016-01 [Member] \| Retained Earnings [Member]
Recently Adopted Accounting Pronouncements [Abstract]
Reclassification of other comprehensive income to retained earnings	208		208
ASU 2016-01 [Member] \| Accumulated Other Comprehensive Loss [Member]
Recently Adopted Accounting Pronouncements [Abstract]
Reclassification of other comprehensive income to retained earnings	$ (208)		$ (208)