RETIREMENT AND OTHER EMPLOYEE BENEFITS (Details 2) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2013 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) item $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2013 USD ($) $ / shares shares
Actual return on plan assets:
Cash-Equivalent Securities with a maturity	1 year
Employee Stock Purchase Plan
Actual return on plan assets:
Common stock purchase price to eligible employees (as a percent)	90.00%
Percentage of Black-Scholes methodology used as a component to calculate value of lookback feature	90.00%
Percentage of maximum subscription price used as a component to calculate value of lookback feature	10.00%
Shares available for issuance | shares				764,645
Subscriptions outstanding (in shares) | shares				58,742	57,369	60,413
Maximum subscription price (in dollars per share) | $ / shares				$ 21.09	$ 21.43	$ 19.58
Shares of stock issued | shares	56,193	56,942	68,099
Stock issuance price (in dollars per share) | $ / shares				$ 21.01	$ 19.58	$ 17.95
Assumptions for valuation of shares
Fair value of grants (in dollars per share) | $ / shares	$ 3.58	$ 3.07	$ 2.78
Risk-free interest rate (as a percent)	0.26%	0.10%	0.14%
Dividend yield (as a percent)	4.40%	4.30%	4.60%
Expected volatility (as a percent)	21.00%	14.00%	14.00%
Expected life in months	12 months	12 months	12 months
Pension Benefits
Fair value measurements of plan assets
Period over which the market-related value is determined	5 years
Number of basic elements on which primary investment goals of the company for pension fund assets are based (in counts) | item				4
Target allocations for plan assets
Cash investment managers generally hold in their portfolios (as a percent)	10.00%
Fund assets measured at fair value
Fair value of plan assets	$ 192,674	$ 186,547	$ 186,547	$ 186,845	$ 192,674	$ 186,547
Percentage of Plan Assets				100.00%	100.00%
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	192,674	186,547
Actual return on plan assets:
Fair value of plan assets at end of year	$ 186,845	192,674	186,547
Pension Benefits | Equity securities
Target allocations for plan assets
Target allocation (as a percent)	72.00%
Pension Benefits | Equity securities | High end of range
Target allocations for plan assets
Target allocation, maximum (as a percent)	80.00%
Pension Benefits | Equity securities | Low end of range
Target allocations for plan assets
Target allocation, minimum (as a percent)	60.00%
Pension Benefits | Common collective trusts - domestic
Fund assets measured at fair value
Fair value of plan assets	$ 48,760	48,760		$ 46,182	$ 48,760
Percentage of Plan Assets				24.70%	25.30%
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	48,760
Actual return on plan assets:
Fair value of plan assets at end of year	46,182	48,760
Pension Benefits | Common collective trusts - international
Fund assets measured at fair value
Fair value of plan assets	42,770	42,770		$ 41,928	$ 42,770
Percentage of Plan Assets				22.50%	22.20%
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	42,770
Actual return on plan assets:
Fair value of plan assets at end of year	41,928	42,770
Pension Benefits | Short term investments
Fund assets measured at fair value
Fair value of plan assets	70	70		$ 71	$ 70
Percentage of Plan Assets				0.00%	0.00%
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	70
Actual return on plan assets:
Fair value of plan assets at end of year	71	70
Pension Benefits | Equity long/short hedge funds
Fund assets measured at fair value
Fair value of plan assets	38,428	38,428		$ 37,970	$ 38,428
Percentage of Plan Assets				20.30%	20.00%
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	38,428
Actual return on plan assets:
Fair value of plan assets at end of year	$ 37,970	38,428
Pension Benefits | Fixed income
Target allocations for plan assets
Target allocation (as a percent)	28.00%
Pension Benefits | Fixed income | High end of range
Target allocations for plan assets
Target allocation, maximum (as a percent)	40.00%
Pension Benefits | Fixed income | Low end of range
Target allocations for plan assets
Target allocation, minimum (as a percent)	20.00%
Pension Benefits | Common collective trust fixed income
Fund assets measured at fair value
Fair value of plan assets	$ 62,646	62,646		$ 60,694	$ 62,646
Percentage of Plan Assets				32.50%	32.50%
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	62,646
Actual return on plan assets:
Fair value of plan assets at end of year	$ 60,694	62,646
Pension Benefits | Comingled bond funds
Fund assets measured at fair value
Maximum high yield	25.00%
Pension Benefits | Significant Other Observable Inputs (Level 2)
Fund assets measured at fair value
Fair value of plan assets	$ 154,246	154,246		$ 148,875	$ 154,246
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	154,246
Actual return on plan assets:
Fair value of plan assets at end of year	148,875	154,246
Pension Benefits | Significant Other Observable Inputs (Level 2) | Common collective trusts - domestic
Fund assets measured at fair value
Fair value of plan assets	48,760	48,760		46,182	48,760
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	48,760
Actual return on plan assets:
Fair value of plan assets at end of year	46,182	48,760
Pension Benefits | Significant Other Observable Inputs (Level 2) | Common collective trusts - international
Fund assets measured at fair value
Fair value of plan assets	42,770	42,770		41,928	42,770
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	42,770
Actual return on plan assets:
Fair value of plan assets at end of year	41,928	42,770
Pension Benefits | Significant Other Observable Inputs (Level 2) | Short term investments
Fund assets measured at fair value
Fair value of plan assets	70	70		71	70
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	70
Actual return on plan assets:
Fair value of plan assets at end of year	71	70
Pension Benefits | Significant Other Observable Inputs (Level 2) | Common collective trust fixed income
Fund assets measured at fair value
Fair value of plan assets	62,646	62,646		60,694	62,646
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	62,646
Actual return on plan assets:
Fair value of plan assets at end of year	60,694	62,646
Pension Benefits | Significant Unobservable Inputs (Level 3)
Fund assets measured at fair value
Fair value of plan assets	38,428	38,428		37,970	38,428
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	38,428
Actual return on plan assets:
Fair value of plan assets at end of year	37,970	38,428
Pension Benefits | Significant Unobservable Inputs (Level 3) | Equity long/short hedge funds
Fund assets measured at fair value
Fair value of plan assets	38,428	36,729	36,729	37,970	38,428	36,729
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	38,428	36,729
Actual return on plan assets:
Relating to assets still held at the reporting date	(458)	1,382
Relating to assets sold during the period		1,491
Purchases		9,700
Sales		(10,874)
Fair value of plan assets at end of year	37,970	38,428	36,729
OPEB
Fund assets measured at fair value
Fair value of plan assets	83,776	79,098	79,098	$ 85,369	$ 83,776	$ 79,098
Percentage of Plan Assets				100.00%	100.00%
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	83,776	79,098
Actual return on plan assets:
Fair value of plan assets at end of year	$ 85,369	83,776	$ 79,098
OPEB | Equity securities
Target allocations for plan assets
Target allocation (as a percent)	60.00%
OPEB | Equity securities | High end of range
Target allocations for plan assets
Target allocation, maximum (as a percent)	76.00%
OPEB | Equity securities | Low end of range
Target allocations for plan assets
Target allocation, minimum (as a percent)	44.00%
OPEB | Common collective trust equity securities
Fund assets measured at fair value
Fair value of plan assets	$ 47,690	47,690		$ 48,553	$ 47,690
Percentage of Plan Assets				56.90%	56.90%
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	47,690
Actual return on plan assets:
Fair value of plan assets at end of year	48,553	47,690
OPEB | Fund assets
Fund assets measured at fair value
Fair value of plan assets	83,851	83,851		$ 85,504	$ 83,851
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	83,851
Actual return on plan assets:
Fair value of plan assets at end of year	$ 85,504	83,851
OPEB | Cash and cash equivalents | High end of range
Target allocations for plan assets
Target allocation (as a percent)	10.00%
OPEB | Fixed income
Target allocations for plan assets
Target allocation (as a percent)	40.00%
OPEB | Fixed income | High end of range
Target allocations for plan assets
Target allocation, maximum (as a percent)	44.00%
OPEB | Fixed income | Low end of range
Target allocations for plan assets
Target allocation, minimum (as a percent)	36.00%
OPEB | Common collective trust fixed income
Fund assets measured at fair value
Fair value of plan assets	$ 33,708	33,708		$ 34,395	$ 33,708
Percentage of Plan Assets				40.30%	40.20%
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	33,708
Actual return on plan assets:
Fair value of plan assets at end of year	34,395	33,708
OPEB | Common collective trusts
Fund assets measured at fair value
Fair value of plan assets	2,453	2,453		$ 2,556	$ 2,453
Percentage of Plan Assets				3.00%	2.90%
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	2,453
Actual return on plan assets:
Fair value of plan assets at end of year	2,556	2,453
OPEB | Payable for securities purchased
Fund assets measured at fair value
Fair value of plan assets	(75)	(75)		$ (135)	$ (75)
Percentage of Plan Assets				(0.20%)	0.00%
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	(75)
Actual return on plan assets:
Fair value of plan assets at end of year	(135)	(75)
OPEB | Significant Other Observable Inputs (Level 2) | Common collective trust equity securities
Fund assets measured at fair value
Fair value of plan assets	47,690	47,690		$ 48,553	$ 47,690
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	47,690
Actual return on plan assets:
Fair value of plan assets at end of year	48,553	47,690
OPEB | Significant Other Observable Inputs (Level 2) | Fund assets
Fund assets measured at fair value
Fair value of plan assets	83,851	83,851		85,504	83,851
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	83,851
Actual return on plan assets:
Fair value of plan assets at end of year	85,504	83,851
OPEB | Significant Other Observable Inputs (Level 2) | Common collective trust fixed income
Fund assets measured at fair value
Fair value of plan assets	33,708	33,708		34,395	33,708
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	33,708
Actual return on plan assets:
Fair value of plan assets at end of year	34,395	33,708
OPEB | Significant Other Observable Inputs (Level 2) | Common collective trusts
Fund assets measured at fair value
Fair value of plan assets	2,453	2,453		$ 2,556	$ 2,453
Fair Value Measurements Using Significant Unobservable Inputs (Level 3)
Fair value of plan assets at beginning of year	2,453
Actual return on plan assets:
Fair value of plan assets at end of year	$ 2,556	$ 2,453
401 (k) plan and ESOP
Employee 401k and Stock Ownership Plan, ESOP Disclosures [Abstract]
Maximum percentage of annual compensation to be deferred by participating employees	25.00%
Shares available to be issued | shares				129,616
Shares contributed | shares	66,783	60,049	64,128
Cash balance formula
Employee 401k and Stock Ownership Plan, ESOP Disclosures [Abstract]
Percentage of each employee's deferrals to be matched	100.00%
Maximum matching contribution as a percentage of employee's eligible compensation	6.00%
Percentage of matching contribution made in shares	3.00%
Average annual basic earnings formula
Employee 401k and Stock Ownership Plan, ESOP Disclosures [Abstract]
Percentage of each employee's deferrals to be matched	50.00%
Maximum matching contribution as a percentage of employee's eligible compensation	3.00%