v3.5.0.2

EMPLOYEE BENEFIT PLANS (Tables) | 6 Months Ended
--- | ---
Jun. 30, 2016
Compensation and Retirement Disclosure [Abstract] |
Schedule of Defined Benefit Plans Disclosures [Table Text Block] | The reconciliation of funded status for the Pension Plans and other postretirement benefit plans as of December 31, 2015 was as follows:
| Pension Plans |  | Other Postretirement Benefits
| (Thousands of Dollars)
Fair value of plan assets | $ | 87,706 |  |  | $ | — |
Less: Benefit obligation | 109,202 |  |  | 10,042 |
Funded status | $ | (21,496 | ) |  | $ | (10,042 | )
Schedule of Net Benefit Costs [Table Text Block] | The following table summarizes the components of net periodic benefit costs for the Pension Plans and other postretirement benefits on a combined basis for periods prior to the Employee Transfer and after the Employee Transfer:
| Pension Plans |  | Other Postretirement Benefits
| 2016 |  | 2015 |  | 2016 |  | 2015
| (Thousands of Dollars)
For the three months ended June 30: |  |  |  |  |  |  |
Service cost | $ | 1,926 |  |  | $ | 1,919 |  |  | $ | 105 |  |  | $ | 118 |
Interest cost | 1,006 |  |  | 1,097 |  |  | 100 |  |  | 111 |
Expected return on assets | (1,351 | ) |  | (1,254 | ) |  | — |  |  | — |
Amortization of prior service credit | (516 | ) |  | (515 | ) |  | (286 | ) |  | (286 | )
Amortization of net loss | 273 |  |  | 461 |  |  | 45 |  |  | 67 |
Net periodic benefit cost (income) | $ | 1,338 |  |  | $ | 1,708 |  |  | $ | (36 | ) |  | $ | 10 |
For the six months ended June 30: |  |  |  |  |  |  |
Service cost | $ | 3,852 |  |  | $ | 3,838 |  |  | $ | 210 |  |  | $ | 236 |
Interest cost | 2,012 |  |  | 2,194 |  |  | 200 |  |  | 223 |
Expected return on assets | (2,703 | ) |  | (2,508 | ) |  | — |  |  | — |
Amortization of prior service credit | (1,033 | ) |  | (1,031 | ) |  | (572 | ) |  | (572 | )
Amortization of net loss | 546 |  |  | 922 |  |  | 90 |  |  | 134 |
Net periodic benefit cost (income) | $ | 2,674 |  |  | $ | 3,415 |  |  | $ | (72 | ) |  | $ | 21 |

X
- References No definition available. + Details
Name: | us-gaap_CompensationAndRetirementDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of one or more of the entity's defined benefit pension plans or one or more other defined benefit postretirement plans, separately for pension plans and other postretirement benefit plans including the entity's schedule of fair value of plan assets for defined benefit or other postretirement plans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e2439-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e2417-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e2410-114920 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=58242635&loc=d3e4179-114921 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 + Details
Name: | us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of the components of net benefit costs for pension plans and/or other employee benefit plans including service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) recognized due to settlements or curtailments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 + Details
Name: | us-gaap_ScheduleOfNetBenefitCostsTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration