BANK PREMISES AND EQUIPMENT (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Total cost	$ 171,227,000	$ 146,762,000
Accumulated depreciation	(76,505,000)	(68,282,000)
Net bank premises and equipment	94,722,000	78,480,000
Depreciation expense	8,500,000	7,300,000	$ 7,000,000
Rental Income, Nonoperating	1,300,000
Operating Leases, Income Statement, Depreciation Expense on Property Subject to or Held-for-lease	939,000
Land [Member]
Property, Plant and Equipment [Line Items]
Total cost	23,719,000	20,585,000
Bank Premises [Member]
Property, Plant and Equipment [Line Items]
Total cost	$ 49,159,000	43,553,000
Bank Premises [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives	5 years
Bank Premises [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives	40 years
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total cost	$ 25,184,000	24,387,000
Leasehold Improvements [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives	1 year
Leasehold Improvements [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives	27 years
Equipment Leased to Other Party [Member]
Property, Plant and Equipment [Line Items]
Total cost	$ 10,644,000
Equipment Leased to Other Party [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives	7 years
Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Total cost	$ 62,521,000	$ 58,237,000
Furniture and Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives	1 year
Furniture and Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives	12 years