ACCUMULATED OTHER COMPREHENSIVE LOSS - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018		Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
AOCI Attributable to Parent, Net of Tax
Beginning balance, net of tax		$ 754,140		$ 518,274	$ 444,062
Income tax benefit (expense)		3,703		(5,374)	10,667
Ending balance, net of tax		731,291		754,140	518,274
Cumulative effect of ASU 2016-01, net of tax		(85)
Retained Earnings
AOCI Attributable to Parent, Net of Tax
Beginning balance, net of tax		32,851		30,098	41,527
Ending balance, net of tax		64,797		32,851	30,098
Cumulative effect of ASU 2016-01, net of tax		(85)
Unrealized Gains (Losses) on Securities
AOCI Attributable to Parent, Net of Tax
Beginning balance, net of tax		(16,295)		(23,708)	(239)
Other comprehensive (loss) income before reclassifications		(21,956)		15,217	(33,699)
Reclassified from accumulated other comprehensive income		3,190	[1]	630	(2,407)
Income tax benefit (expense)		3,941		(5,546)	12,637
Net current-period other comprehensive (loss) income, net of tax		(14,825)		10,301	(23,469)
Reclassification of certain deferred tax effects	[2]			(2,888)
Ending balance, net of tax		(31,120)		(16,295)	(23,708)
Unrealized Gains (Losses) on Derivatives
AOCI Attributable to Parent, Net of Tax
Beginning balance, net of tax		6,399		4,595	0
Other comprehensive (loss) income before reclassifications		2,351		276	5,255
Reclassified from accumulated other comprehensive income		(1,406)		754	1,815
Income tax benefit (expense)		(198)		(360)	(2,475)
Net current-period other comprehensive (loss) income, net of tax		747		670	4,595
Reclassification of certain deferred tax effects	[2]			1,134
Ending balance, net of tax		7,146		6,399	4,595
Net Prior Service (Cost) Credit
AOCI Attributable to Parent, Net of Tax
Reclassified from accumulated other comprehensive income	[3]	(7)		(8)	(8)
Net Gain (Loss)
AOCI Attributable to Parent, Net of Tax
Reclassified from accumulated other comprehensive income	[3]	2,189		1,613	1,828
Total
AOCI Attributable to Parent, Net of Tax
Beginning balance, net of tax		(36,298)		(38,493)	(18,683)
Other comprehensive (loss) income before reclassifications		(21,599)		10,283	(31,705)
Reclassified from accumulated other comprehensive income		3,966	[1]	2,989	1,228
Income tax benefit (expense)		3,703		(5,374)	10,667
Net current-period other comprehensive (loss) income, net of tax		(13,930)		7,898	(19,810)
Reclassification of certain deferred tax effects	[2]			(5,703)
Ending balance, net of tax		(50,228)		(36,298)	(38,493)
Accounting Standards Update 2016-01 | Retained Earnings
AOCI Attributable to Parent, Net of Tax
Cumulative Effect of New Accounting Principle in Period of Adoption, Before Tax						$ (107)
Cumulative effect of ASU 2016-01, net of tax						$ (85)
Defined Benefit Pension Plan | Net Prior Service (Cost) Credit
AOCI Attributable to Parent, Net of Tax
Beginning balance, net of tax		(133)		(133)	(44)
Other comprehensive (loss) income before reclassifications		0		8	(129)
Reclassified from accumulated other comprehensive income		(7)		(8)	(8)
Income tax benefit (expense)		1		0	48
Net current-period other comprehensive (loss) income, net of tax		(6)		0	(89)
Reclassification of certain deferred tax effects	[2]			0
Ending balance, net of tax		(139)		(133)	(133)
Defined Benefit Pension Plan | Net Gain (Loss)
AOCI Attributable to Parent, Net of Tax
Beginning balance, net of tax		(26,269)		(19,247)	(18,400)
Other comprehensive (loss) income before reclassifications		(1,994)		(5,218)	(3,132)
Reclassified from accumulated other comprehensive income		2,189		1,613	1,828
Income tax benefit (expense)		(41)		532	457
Net current-period other comprehensive (loss) income, net of tax		154		(3,073)	(847)
Reclassification of certain deferred tax effects	[2]			(3,949)
Ending balance, net of tax		$ (26,115)		$ (26,269)	$ (19,247)

[1] As discussed in “Note 1 – Summary of Significant Accounting and Reporting Policies,” the Company adopted ASU 2016-01 on January 1, 2018. This amount includes a reclassification for the cumulative adjustment to retained earnings of $107,000 ($85,000, net of tax).

[2] Amounts reclassified to retained earnings due to early adoption of ASU 2018-02. See “Note 1 – Summary of Significant Accounting and Reporting Policies” for further information.

[3] These accumulated other comprehensive income components are included in the computation of net periodic pension cost (income) presented in “Note 11 - Employee Benefits.”