SEGMENT INFORMATION (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Information about reportable segments
Net interest income	$ 67,274	$ 66,881
Provision for loan losses	1,828	1,341
Noninterest revenues	44,318	38,281
Amortization of intangible assets	2,768	1,442
Acquisition expenses	1,716	77
Other operating expenses	69,091	66,150
Income before income taxes	36,189	36,152
Assets	8,913,860	8,615,901	$ 8,666,437
Goodwill	542,986	465,142	$ 465,142
Eliminations [Member]
Information about reportable segments
Net interest income	0	0
Provision for loan losses	0	0
Noninterest revenues	(664)	(566)
Amortization of intangible assets	0	0
Acquisition expenses	0	0
Other operating expenses	(664)	(566)
Income before income taxes	0	0
Assets	(43,145)	(38,665)
Goodwill	0	0
Banking [Member] | Operating Segments [Member]
Information about reportable segments
Net interest income	67,134	66,798
Provision for loan losses	1,828	1,341
Noninterest revenues	15,867	15,313
Amortization of intangible assets	554	719
Acquisition expenses	521	70
Other operating expenses	49,493	48,460
Income before income taxes	30,605	31,521
Assets	8,663,042	8,546,646
Goodwill	440,870	440,870
Employee Benefit Services [Member] | Operating Segments [Member]
Information about reportable segments
Net interest income	78	40
Provision for loan losses	0	0
Noninterest revenues	17,636	12,390
Amortization of intangible assets	1,591	116
Acquisition expenses	1,062	0
Other operating expenses	11,370	9,447
Income before income taxes	3,691	2,867
Assets	221,437	38,535
Goodwill	84,213	8,019
All Other [Member]
Information about reportable segments
Net interest income	62	43
Provision for loan losses	0	0
Noninterest revenues	11,479	11,144
Amortization of intangible assets	623	607
Acquisition expenses	133	7
Other operating expenses	8,892	8,809
Income before income taxes	1,893	1,764
Assets	72,526	69,385
Goodwill	$ 17,903	$ 16,253