EMPLOYEE BENEFITS (Tables)

12 Months Ended

Dec. 31, 2017

Retirement Benefits [Abstract]

Summary of Actual and Target Asset Allocation of Plan Assets

The following is a summary of the pension plan's actual and target asset allocations at December 31, 2017 and 2016 by asset category:

									Target
Pension Plan Assets	2017		% of Total		2016		% of Total		Allocation
Fixed maturity securities - corporate bonds	$	11,003	7.0	%	$	9,451	7.4	%	0	%	-	15	%
Redeemable preferred stock	3,216		2.0		3,144		2.4		0	%	-	10	%
Equity securities	87,603		55.6		69,770		54.3		50	%	-	70	%
Pooled separate accounts
Core plus bond separate account fund	17,948		11.4		10,401		8.1		0	%	-	40	%
U.S. property separate account fund	15,502		9.8		14,330		11.1		0	%	-	25	%
Arbitrage fund	8,506		5.4		8,292		6.5		0	%	-	10	%
United Life annuity	9,846		6.2		9,377		7.3		5	%	-	10	%
Cash and cash equivalents	4,020		2.6		3,665		2.9		0	%	-	10	%
Total plan assets	$	157,644	100.0	%	$	128,430	100.0	%

Categories of Pension Plan Assets at Fair Value on Recurring Basis

The following tables present the categorization of the pension plan's assets measured at fair value on a recurring basis at December 31, 2017 and 2016:

			Fair Value Measurements
Description	December 31, 2017		Level 1		Level 2		Level 3
Fixed maturity securities - corporate bonds	$	11,003	$	—	$	11,003	$	—
Redeemable preferred stock	3,216		3,216		—		—
Equity securities	87,603		87,603		—		—
Pooled separate accounts
Core plus bond separate account fund	17,948		—		17,948		—
U.S. property separate account fund	15,502		—		—		15,502
Arbitrage fund	8,506		—		8,506		—
Money market funds	4,011		4,011		—		—
Total assets measured at fair value	$	147,789	$	94,830	$	37,457	$	15,502

			Fair Value Measurements
Description	December 31, 2016		Level 1		Level 2		Level 3
Fixed maturity securities - corporate bonds	$	9,451	$	—	$	9,451	$	—
Redeemable preferred stock	3,144		3,144		—		—
Equity securities	69,770		69,770		—		—
Pooled separate accounts
Core plus bond separate account fund	10,401		—		10,401		—
U.S. property separate account fund	14,330		—		—		14,330
Arbitrage fund	8,292		—		8,292		—
Money market funds	3,659		3,659		—		—
Total assets measured at fair value	$	119,047	$	76,573	$	28,144	$	14,330

Summary of Changes in Fair Value of Pension Plan Securities

The following tables provide a summary of the changes in fair value of the pension plan's Level 3 securities:

	U.S. property separate account fund
Balance at January 1, 2017	$	14,330
Unrealized gains	1,172
Balance at December 31, 2017	$	15,502

	U.S. property separate account fund
Balance at January 1, 2016	$	11,252
Unrealized gains	1,078
Purchases	2,000
Balance at December 31, 2016	$	14,330

Schedule of Actuarial Assumptions Used

The following actuarial assumptions were used to determine the reported plan benefit obligations at December 31:

Weighted-average assumptions as of	Pension Benefits				Post-retirement Benefits
December 31,	2017		2016		2017		2016
Discount rate	3.65	%	4.17	%	3.65	%	4.17	%
Rate of compensation increase	3.00		3.00		N/A		N/A

The following actuarial assumptions were used at January 1 to determine our reported net periodic benefit costs for the year ended December 31:

Weighted-average assumptions as of	Pension Benefits						Post-retirement Benefits
January 1,	2017		2016		2015		2017		2016		2015
Discount rate	4.17	%	4.21	%	3.86	%	4.17	%	4.21	%	3.86	%
Expected long-term rate of return on plan assets	7.50		7.50		7.50		N/A		N/A		N/A
Rate of compensation increase	3.00		3.00		3.00		N/A		N/A		N/A

Schedule of Health Care Cost Trend Rates

	Health Care Benefits				Dental Claims
Years Ended December 31,	2017		2016		2017		2016
Health care cost trend rates assumed for next year	7.00	%	7.00	%	4.00	%	4.00	%
Rate to which the health care trend rate is assumed to decline (ultimate trend rate)	4.50	%	4.50	%	N/A		N/A
Year that the rate reaches the ultimate trend rate	2026		2025		N/A		N/A

Schedule of Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates

A 1.0 percent change in assumed health care cost trend rates would have the following effects:

	1% Increase		1% Decrease
Effect on the net periodic post-retirement health care benefit cost	$	1,126	$	(883	)
Effect on the accumulated post-retirement benefit obligation	9,487		(7,698		)

Reconciliation of Benefit Obligations, Plan Assets, and Funded Status

The following table provides a reconciliation of benefit obligations, plan assets and funded status of our plans:

	Pension Benefits						Post-retirement Benefits
Years Ended December 31,	2017			2016			2017			2016
Reconciliation of benefit obligation
Benefit obligation at beginning of year	$	171,876		$	160,390		$	46,785		$	72,175
Service cost	6,857			6,490			2,021			3,728
Interest cost	7,060			6,654			1,927			3,015
Actuarial loss	26,963			2,215			6,326			1,468
Adjustment for plan amendment	—			—			—			(32,289		)
Benefit payments	(4,407		)	(3,873		)	(1,331		)	(1,312		)
Benefit obligation at end of year (1)	$	208,349		$	171,876		$	55,728		$	46,785
Reconciliation of fair value of plan assets
Fair value of plan assets at beginning of year	$	128,430		$	106,600		$	—		$	—
Actual return on plan assets	22,225			9,320			—			—
Employer contributions	11,396			16,383			1,331			1,311
Benefit payments	(4,407		)	(3,873		)	(1,331		)	(1,311		)
Fair value of plan assets at end of year	$	157,644		$	128,430		$	—		$	—
Funded status at end of year	$	(50,705	)	$	(43,446	)	$	(55,728	)	$	(46,785	)

(1) For the pension plan, the benefit obligation is the projected benefit obligation. For the post-retirement benefit plan, the benefit obligation is the accumulated post-retirement benefit obligation.

Schedule of Amounts Recognized in AOCI

The following table displays the effect that the unrecognized prior service cost and unrecognized actuarial loss of our plans had on accumulated other comprehensive income ("AOCI"), as reported in the accompanying Consolidated Balance Sheets:

	Pension Benefits				Post-retirement Benefits
Years Ended December 31	2017		2016		2017			2016
Amounts recognized in AOCI
Unrecognized prior service cost	$	—	$	—	$	(26,880	)	$	(32,289	)
Unrecognized actuarial (gain) loss	60,571		49,745		25,235			20,756
Total amounts recognized in AOCI	$	60,571	$	49,745	$	(1,645	)	$	(11,533	)

Components of Net Periodic Benefit Cost

The components of the net periodic benefit cost for our pension and post-retirement benefit plans are as follows:

	Pension Plan									Post-retirement Benefit Plan
Years Ended December 31,	2017			2016			2015			2017			2016		2015
Net periodic benefit cost
Service cost	$	6,857		$	6,490		$	6,675		$	2,021		$	3,728	$	5,220
Interest cost	7,060			6,654			5,999			1,927			3,015		2,856
Expected return on plan assets	(9,650		)	(7,952		)	(7,800		)	—			—		—
Amortization of prior service cost	—			—			—			(5,409		)	—		—
Amortization of net loss	3,562			3,968			4,546			1,846			1,518		2,920
Net periodic benefit cost	$	7,829		$	9,160		$	9,420		$	385		$	8,261	$	10,996

Summary of Expected Benefit Payments

The following table summarizes the expected benefits to be paid from our plans over the next 10 years:

	2018		2019		2020		2021		2022		2023 - 2027
Pension benefits	$	5,620	$	6,140	$	6,780	$	7,520	$	8,240	$	52,950
Post-retirement benefits	$	1,350	$	1,540	$	1,700	$	1,880	$	2,050	$	13,310