INCOME TAXES - PROVISION AND DEFERRED TAX (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current expense:
Federal									$ 24,295	$ 18,108	$ 22,143
State									465	1,125	2,469
Deferred expense:
Federal									(1,753)	(1,262)	(8,637)
State									53	107	(447)
Total	$ 4,960	$ 4,848	$ 4,359	$ 8,893	$ 3,844	$ 3,119	$ 4,154	$ 6,961	$ 23,060	$ 18,078	$ 15,528
Effective tax rate that differs from that computed at the federal statutory rate
Federal statutory rate times financial statement income									35.00%	35.00%	35.00%
Effect of:
State taxes, net of federal benefit (as a percent)									0.49%	1.50%	2.96%
General business tax credits (as a percent)									(0.33%)	(0.43%)	(0.67%)
Nontaxable income									(2.12%)	(2.68%)	(2.80%)
Other, net (as a percent)									0.39%	0.56%	0.55%
Effective tax rate									33.43%	33.95%	35.04%
Deferred tax assets:
Allowance for loan and leases losses	10,824				9,595				$ 10,824	$ 9,595
Accrued expenses	5,733				3,913				5,733	3,913
Net operating loss carryforward	5,417				1,574				5,417	1,574
Depreciation					1,289					1,289
Other-than-temporary impairment	746				750				746	750
Partnership losses	879				842				879	842
OREO Writedowns	19				20				19	20
Fair value of cash flow hedges	138				210				138	210
Acquisition fair value adjustments	1,379								1,379
Other	2,237				2,061				2,237	2,061
Total deferred tax assets	27,372				20,254				27,372	20,254
Deferred tax liabilities:
Unrealized investment securities gains	(711)				(1,314)				(711)	(1,314)
Federal Home Loan Bank dividends	(4,296)				(4,315)				(4,296)	(4,315)
Deferred loan fees	(162)				(317)				(162)	(317)
Mortgage servicing rights	(1,870)				(1,781)				(1,870)	(1,781)
Bargain purchase gain	(1,436)				(552)				(1,436)	(552)
New market tax credits	(831)				(707)				(831)	(707)
Depreciation and amortization	(138)								(138)
Other	(1,127)				(374)				(1,127)	(374)
Total deferred tax liabilities	(10,571)				(9,360)				(10,571)	(9,360)
Less: Valuation allowance	(1,635)				(1,564)				(1,635)	(1,564)
Net deferred tax asset	$ 15,166				$ 9,330				$ 15,166	$ 9,330