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Employee Benefit Plans - Additional Information (Detail) kr in Millions |  |  | 1 Months Ended | 3 Months Ended | 6 Months Ended | 9 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Dec. 01, 2015 USD ($) | Nov. 30, 2015 | May 31, 2018 USD ($) | Apr. 30, 2018 USD ($) | Dec. 31, 2017 Person | Jan. 02, 2016 | Dec. 31, 2015 | Dec. 31, 2010 Person | Jun. 30, 2018 NOK (kr) | Jun. 30, 2018 USD ($) | Jun. 30, 2017 NOK (kr) | Jun. 30, 2017 USD ($) | Jun. 30, 2018 NOK (kr) | Jun. 30, 2018 USD ($) | Jun. 30, 2017 NOK (kr) | Jun. 30, 2017 USD ($) | Dec. 31, 2017 NOK (kr) Person | Dec. 31, 2017 USD ($) Person | Mar. 31, 2017 NOK (kr) | Mar. 31, 2017 USD ($) | Mar. 31, 2016 USD ($) | Dec. 31, 2018 USD ($)
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of employers participated in defined benefit plan | Person |  |  |  |  | 4 |  |  | 60 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of employers still remains in defined benefit plan | Person |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 30 | 30 |  |  |  |
Additional estimated net periodic benefit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3.80% | 3.80% |  |  |  |
Defined benefit plan, significant concentrations of risk |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | U.S. Plans The pension plan and the supplemental plan assets are periodically evaluated for concentration risks. As of December 31, 2017, the company did not have any individual asset investments that comprised 10% or more of each planâ€™s overall assets. | U.S. Plans The pension plan and the supplemental plan assets are periodically evaluated for concentration risks. As of December 31, 2017, the company did not have any individual asset investments that comprised 10% or more of each planâ€™s overall assets. |  |  |  |
Defined benefit plan, concentration risk, assets, equity securities, difference plan assets and liabilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 15.00% | 15.00% |  |  |  |
Defined benefit plan, concentration risk, assets, equity securities, maximum foreign and us stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10.00% | 10.00% |  |  |  |
Defined benefit plan, concentration risk, diversification, equity limit, single industry |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 25.00% | 25.00% |  |  |  |
Defined benefit plan, concentration risk, diversification, equity limit, single corporation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10.00% | 10.00% |  |  |  |
Defined benefit plan, concentration risk, diversification, debt limit, single issuer |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10.00% | 10.00% |  |  |  |
Defined contribution plan, description |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | Effective January 1, 2018, the company no longer provides a matching of 50% of the first 8% of eligible compensation in an attempt to reduce costs. | Effective January 1, 2018, the company no longer provides a matching of 50% of the first 8% of eligible compensation in an attempt to reduce costs. |  |  |  |
Pension Plans, Defined Benefit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Defined benefit plan, employer contributions |  |  |  |  |  |  |  |  |  | $ 0 |  | $ 0 |  | $ 0 |  | $ 0 |  | $ 0 |  | $ 3,000,000 | $ 0 |
Supplemental Executive Retirement Plan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Defined benefit plan, employer contributions |  |  |  |  |  |  |  |  |  | 40,000 |  | 0 |  | 300,000 |  | 0 |  | $ 100,000 |  | 200,000 |  |
Expected contribution to the plan during the remaining quarters of fiscal 2018 |  |  |  |  |  |  |  |  |  | 700,000 |  |  |  | 700,000 |  |  |  |  |  |  |  |
Norway`s Defined Benefit Pension Plan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of employers still remains in defined benefit plan | Person |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 90 | 90 |  |  |  |
Defined benefit plan, employer contributions |  |  |  |  |  |  |  |  | kr 1.9 | 200,000 | kr 3.0 | $ 400,000 | kr 1.9 | 200,000 | kr 3.0 | $ 400,000 | kr 2.7 | $ 300,000 | kr 3.6 | $ 400,000 |  |
Expected contribution to the plan during the remaining quarters of fiscal 2018 |  |  |  |  |  |  |  |  |  | 0 |  |  |  | $ 0 |  |  |  |  |  |  |  |
Retirement Contributions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Defined contribution plan, company contribution percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3.00% | 3.00% |  |  |  |
Defined contribution plan, company contribution, vesting period, years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5 years | 5 years |  |  |  |
Retirement Contributions | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Defined contribution plan, company contribution percentage additional percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1.00% | 1.00% |  |  |  |
Retirement Contributions | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Defined contribution plan, company contribution percentage additional percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 8.00% | 8.00% |  |  |  |
Defined Contribution Savings Plan 401k |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Defined contribution plan, company contribution, vesting period, years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5 years | 5 years |  |  |  |
Percentage of defined plan, minimum employee contribution |  |  |  |  | 2.00% |  |  |  |  |  |  |  |  |  |  |  | 2.00% | 2.00% |  |  |  |
Percentage of defined plan, maximum employee contribution |  |  |  |  | 75.00% |  |  |  |  |  |  |  |  |  |  |  | 75.00% | 75.00% |  |  |  |
Percentage of defined plan, company contribution match, cash |  |  |  |  |  | 50.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of defined plan, company contribution match, employee deferred compensation |  |  |  |  |  | 8.00% | 8.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Defined contribution plan, company contribution percentage match, company stock |  |  |  |  |  |  | 50.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Non-Qualified Supplemental Savings Plan Executives |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Defined contribution plan, company contribution percentage match, common stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 50.00% | 50.00% |  |
Deferred compensation arrangement with individual, deferred compensation percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 50.00% | 50.00% |  |
Deferred compensation arrangement with individual, deferred bonus percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 100.00% | 100.00% |  |
Defined contribution plan, restoration benefit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3.00% | 3.00% |  |
Non-Qualified Supplemental Savings Plan Executives | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Defined contribution plan, company contribution percentage additional percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1.00% | 1.00% |  |
Non-Qualified Supplemental Savings Plan Executives | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Defined contribution plan, company contribution percentage additional percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 8.00% | 8.00% |  |
Multinational Retirement Plan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Defined contribution plan, company contribution, vesting period, years | 5 years | 6 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of defined plan, minimum employee contribution | 1.00% | 1.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of defined plan, maximum employee contribution | 50.00% | 15.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of defined plan, company contribution match, cash | 50.00% | 50.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of defined plan, company contribution match, employee deferred compensation | 600.00% | 6.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reduction in defined plan assets and liabilities | $ 6,400,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Scenario, Forecast | President, and Chief Executive Officer | Supplemental Executive Retirement Plan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement of distribution |  |  |  | $ 9,600,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement loss |  |  |  | $ 500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Supplemental Executive Retirement Plan | President, and Chief Executive Officer |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement of distribution |  |  | $ 8,900,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Settlement loss |  |  |  |  |  |  |  |  |  | $ 300,000 |  |  |  |  |  |  |  |  |  |  |  |
Postretirement Benefit Plan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Additional estimated net periodic benefit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 2,000,000 |  |
Postretirement Benefit Plan | Scenario, Forecast |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Postretirement benefit plan obligations reduction |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,900,000

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- Definition Description of investment policy and strategy for defined benefit plan asset. Includes, but is not limited to, investment allocation decision and factor pertinent to understanding investment policy and strategy for plan asset. Factor includes, but is not limited to, investment goal, risk management practice, permitted and prohibited investment including use of derivative, diversification, and relationship between plan asset and obligation. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=112275985&loc=d3e4179-114921 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(i) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 + Details
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